Change Total Number of Pages

We've created an invoice template and printing Terms and Condition on the last page. We added Page X of  Y (Total Pages) its counting T&C page in the total as well but we would like to skip that from total no of pages. T&C is in its own section. I've tried few things but with no help.

I already tried adding Page { PAGE } of { = { NUMPAGES} -1 }  and even used SECTIONPAGES but its not working. NUMPAGES on its own works but even if i add -1 it still show the total number of pages.

I would really appreciate if any one can help.