XPATH query using value from xml

I am trying to return the result of the Filename node that matches the loopcounter value.

I have tried variations of concat(//Filename[//loopcounter/text()],/text())

<?xml version="1.0" encoding="UTF-8"?>
<ProcessData>
  <PrimaryDocument SCIObjectID="IDCEDI98:node1:15c5a08563f:2012534"/>
  <Mail_Client>
    <Headers>
      <Attachment_Count>1</Attachment_Count>
    </Headers>
    <Attachments>
      <ContentTypes>
        <Content_Type1>text/plain;
    name="TOYEDI_20170530000003.TXT_14665218_2017May29.TXT"</Content_Type1>
      </ContentTypes>
      <Filenames>
        <Filename1>TOYEDI_20170530000003.TXT_14665218_2017May29.TXT</Filename1>
      </Filenames>
      <FileExtensions>
        <FileExtension1>TXT</FileExtension1>
      </FileExtensions>
    </Attachments>
  </Mail_Client>
  <b2b-raw-message>true</b2b-raw-message>
  <b2b-protocol>smtp</b2b-protocol>
  <loopcounter>1</loopcounter>
  <TINA>
    <MAILBOX>
      <WORKFLOW_ID>5344652</WORKFLOW_ID>
      <TIME_STAMP>2017Jun02</TIME_STAMP>
    </MAILBOX>
  </TINA>
  <DestinationMessageName/>
</ProcessData>