How to get index of node based on node value using XSLT

Hi ,

I want to get the index of node based on node value USING XSLT. I have this xml-

<Response>

<value>B</value>

<value>A</value>

<value>C</value>

</Response>

Now if i will pass 'A' then it should return index of node  means -2 .

Thanks in advance.