XPath Count function always return 0.0

I'm using below xml to get the count of tag 'c'.

<?xml version='1.0' encoding='UTF-8'?>
<xyz xmlns=".....">
<a>
  <b>
    <c>X:1 Y:0</c>
    <c>X:1 Y:0</c>
    <c>X:2 Y:0</c>
  </b>
  <b>
    <c>X:1 Y:0</c>
    <c>X:2 Y:0</c>
  </b>
</a>
</xyz>

Below is my java code :

xpath = factory.newXPath();
xpr = xpath.compile("count(//xyz/a/b/c)");
System.out.println(xpr.evaluate(inputSource, XPathConstants.NUMBER));

But the above code always returns 0.0

Am I doing something wrong ?