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    <link:label id="lab_us-gaap_CashAndCashEquivalentsAtCarryingValue_F5D1034B49C4C1BB4FFDE0F691ADA4C4_terseLabel_en-US" xlink:label="lab_us-gaap_CashAndCashEquivalentsAtCarryingValue_F5D1034B49C4C1BB4FFDE0F691ADA4C4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Cash and cash equivalents</link:label>
    <link:label id="lab_us-gaap_CashAndCashEquivalentsAtCarryingValue_F5D1034B49C4C1BB4FFDE0F691ADA4C4_label_en-US" xlink:label="lab_us-gaap_CashAndCashEquivalentsAtCarryingValue_F5D1034B49C4C1BB4FFDE0F691ADA4C4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Cash and Cash Equivalents, at Carrying Value</link:label>
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_F5D1034B49C4C1BB4FFDE0F691ADA4C4" xlink:to="lab_us-gaap_CashAndCashEquivalentsAtCarryingValue_F5D1034B49C4C1BB4FFDE0F691ADA4C4" xlink:type="arc" />
    <link:label id="lab_us-gaap_AccountsReceivableNetCurrent_CDD847625C44DD4C08CCE0F691ADC59D_terseLabel_en-US" xlink:label="lab_us-gaap_AccountsReceivableNetCurrent_CDD847625C44DD4C08CCE0F691ADC59D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Accounts receivable, net of allowance for doubtful accounts of $425 and $325</link:label>
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    <link:label id="lab_us-gaap_InventoryNet_388245DC34AAFF9A2F71E0F691AE3015_terseLabel_en-US" xlink:label="lab_us-gaap_InventoryNet_388245DC34AAFF9A2F71E0F691AE3015" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Inventories, net</link:label>
    <link:label id="lab_us-gaap_InventoryNet_388245DC34AAFF9A2F71E0F691AE3015_label_en-US" xlink:label="lab_us-gaap_InventoryNet_388245DC34AAFF9A2F71E0F691AE3015" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Inventory, Net</link:label>
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    <link:label id="lab_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_E625428948C50C844C21E0F691AE2A07_label_en-US" xlink:label="lab_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_E625428948C50C844C21E0F691AE2A07" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Prepaid Expense and Other Assets, Current</link:label>
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    <link:label id="lab_us-gaap_AssetsCurrent_5DD8E607E9AF4BC502B0E0F691AE92F8_totalLabel_en-US" xlink:label="lab_us-gaap_AssetsCurrent_5DD8E607E9AF4BC502B0E0F691AE92F8" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Total current assets</link:label>
    <link:label id="lab_us-gaap_AssetsCurrent_5DD8E607E9AF4BC502B0E0F691AE92F8_label_en-US" xlink:label="lab_us-gaap_AssetsCurrent_5DD8E607E9AF4BC502B0E0F691AE92F8" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Assets, Current</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentNet_A2D80F9C2F0E5DBB89E8E0F691AEA536_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentNet_A2D80F9C2F0E5DBB89E8E0F691AEA536" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Property, plant and equipment, net of accumulated depreciation of $304,366 and $288,607</link:label>
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    <link:label id="lab_us-gaap_Goodwill_B75A22C29D006A36941EE0F691AF7E89_label_en-US" xlink:label="lab_us-gaap_Goodwill_B75A22C29D006A36941EE0F691AF7E89" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Goodwill</link:label>
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    <link:label id="lab_us-gaap_OtherNoncashIncomeExpense_571C6B92A1DCA7110814E0F692B8D5A9_label_en-US" xlink:label="lab_us-gaap_OtherNoncashIncomeExpense_571C6B92A1DCA7110814E0F692B8D5A9" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Other Noncash Income (Expense)</link:label>
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_9983E9B1DE1F37CE4365E0F692B8B9DE" xlink:to="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_9983E9B1DE1F37CE4365E0F692B8B9DE" xlink:type="arc" />
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInAccountsAndNotesReceivable_4E54D4BAD14D9610ED8FE0F692B87F8A" xlink:to="lab_us-gaap_IncreaseDecreaseInAccountsAndNotesReceivable_4E54D4BAD14D9610ED8FE0F692B87F8A" xlink:type="arc" />
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_106705AF73C81B76F26CE0F692B9ABCB" xlink:type="locator" />
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    <link:label id="lab_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_9BCB554367D16428ED91E0F692B940F0_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_9BCB554367D16428ED91E0F692B940F0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Increase in income taxes payable</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_560FFC8644FAEEC84712E0F691EB40CD" xlink:type="locator" />
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_3FAF5BE0430C77086687E0F691EB8B1F_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_3FAF5BE0430C77086687E0F691EB8B1F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Exercised (in usd per share)</link:label>
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    <link:loc xlink:href="nx-20190430.xsd#nx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:label="loc_nx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_D8A4399EB1FCD95839DAE0F691EC9AF3" xlink:type="locator" />
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    <link:label id="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687_terseLabel_en-US" xlink:label="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Sell CAD, buy USD</link:label>
    <link:label id="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687_label_en-US" xlink:label="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Sell CAD [Member]</link:label>
    <link:label id="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687_documentation_en-US" xlink:label="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Sell CAD [Member]</link:label>
    <link:loc xlink:href="nx-20190430.xsd#nx_SellCADMember" xlink:label="loc_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687" xlink:to="lab_nx_SellCADMember_5CE4BFDAD2D4B81490ADE0F69152F687" xlink:type="arc" />
    <link:label id="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5_terseLabel_en-US" xlink:label="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Sell GBP, buy USD</link:label>
    <link:label id="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5_label_en-US" xlink:label="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Sell GBP [Member]</link:label>
    <link:label id="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5_documentation_en-US" xlink:label="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Sell GBP [Member]</link:label>
    <link:loc xlink:href="nx-20190430.xsd#nx_SellGBPMember" xlink:label="loc_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5" xlink:to="lab_nx_SellGBPMember_33581095FDAFC357922BE0F69152BEC5" xlink:type="arc" />
    <link:label id="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D_terseLabel_en-US" xlink:label="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Buy EUR, sell GBP</link:label>
    <link:label id="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D_label_en-US" xlink:label="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Buy EUR, sell GBP [Member]</link:label>
    <link:label id="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D_documentation_en-US" xlink:label="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Buy EUR, sell GBP [Member]</link:label>
    <link:loc xlink:href="nx-20190430.xsd#nx_BuyEurSellGbpMember" xlink:label="loc_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D" xlink:to="lab_nx_BuyEurSellGbpMember_1F912974774C429BC935E0F69152787D" xlink:type="arc" />
    <link:label id="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC_terseLabel_en-US" xlink:label="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Buy USD, Sell EUR</link:label>
    <link:label id="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC_label_en-US" xlink:label="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Buy USD, Sell EUR [Member]</link:label>
    <link:label id="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC_documentation_en-US" xlink:label="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Buy USD, Sell EUR</link:label>
    <link:loc xlink:href="nx-20190430.xsd#nx_BuyUSDSellEURMember" xlink:label="loc_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC" xlink:to="lab_nx_BuyUSDSellEURMember_1A3911C7E0727DDF253FE0F691523BAC" xlink:type="arc" />
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    <link:label id="lab_us-gaap_DerivativesFairValueLineItems_4A8DFD52D622F3C8146AE0F691520617_label_en-US" xlink:label="lab_us-gaap_DerivativesFairValueLineItems_4A8DFD52D622F3C8146AE0F691520617" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Derivatives, Fair Value [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativesFairValueLineItems" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_4A8DFD52D622F3C8146AE0F691520617" xlink:type="locator" />
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    <link:label id="lab_invest_DerivativeNotionalAmount_FA00252FFE1078BB605EE0F69153426C_label_en-US" xlink:label="lab_invest_DerivativeNotionalAmount_FA00252FFE1078BB605EE0F69153426C" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Derivative, Notional Amount</link:label>
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="loc_invest_DerivativeNotionalAmount_FA00252FFE1078BB605EE0F69153426C" xlink:type="locator" />
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAtFairValueNet" xlink:label="loc_us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAtFairValueNet_1F882210C11E971F3E16E0F6915358AF" xlink:type="locator" />
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    <link:label id="lab_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_E13D02D42148B4BA0226E0F6931CAEFC_label_en-US" xlink:label="lab_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_E13D02D42148B4BA0226E0F6931CAEFC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Allowance for Doubtful Accounts Receivable, Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_E13D02D42148B4BA0226E0F6931CAEFC" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_E13D02D42148B4BA0226E0F6931CAEFC" xlink:to="lab_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_E13D02D42148B4BA0226E0F6931CAEFC" xlink:type="arc" />
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    <link:label id="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_CE9362D1210B85239210E0F6931C824F_label_en-US" xlink:label="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_CE9362D1210B85239210E0F6931C824F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_CE9362D1210B85239210E0F6931C824F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_CE9362D1210B85239210E0F6931C824F" xlink:to="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_CE9362D1210B85239210E0F6931C824F" xlink:type="arc" />
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    <link:label id="lab_us-gaap_PreferredStockNoParValue_E2255873A992B189455BE0F6931D4086_label_en-US" xlink:label="lab_us-gaap_PreferredStockNoParValue_E2255873A992B189455BE0F6931D4086" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Preferred Stock, No Par Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PreferredStockNoParValue" xlink:label="loc_us-gaap_PreferredStockNoParValue_E2255873A992B189455BE0F6931D4086" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PreferredStockNoParValue_E2255873A992B189455BE0F6931D4086" xlink:to="lab_us-gaap_PreferredStockNoParValue_E2255873A992B189455BE0F6931D4086" xlink:type="arc" />
    <link:label id="lab_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7_terseLabel_en-US" xlink:label="lab_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Preferred stock, shares authorized</link:label>
    <link:label id="lab_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7_label_en-US" xlink:label="lab_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Preferred Stock, Shares Authorized</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7" xlink:to="lab_us-gaap_PreferredStockSharesAuthorized_7BB61AE350839AD4B36AE0F6931D79A7" xlink:type="arc" />
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    <link:label id="lab_us-gaap_PreferredStockSharesIssued_F831117412721347F690E0F6931D2059_label_en-US" xlink:label="lab_us-gaap_PreferredStockSharesIssued_F831117412721347F690E0F6931D2059" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Preferred Stock, Shares Issued</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="loc_us-gaap_PreferredStockSharesIssued_F831117412721347F690E0F6931D2059" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PreferredStockSharesIssued_F831117412721347F690E0F6931D2059" xlink:to="lab_us-gaap_PreferredStockSharesIssued_F831117412721347F690E0F6931D2059" xlink:type="arc" />
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    <link:label id="lab_us-gaap_PreferredStockSharesOutstanding_3E409E6B6589597E0011E0F6931DCAA7_label_en-US" xlink:label="lab_us-gaap_PreferredStockSharesOutstanding_3E409E6B6589597E0011E0F6931DCAA7" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Preferred Stock, Shares Outstanding</link:label>
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