Calculate Grand Total with Conditional

[fpavan76]

Hi to all,
I need a suggest about a measure to calculate grand total with particular condition.

I have 3 columns A, B and C
I want insert this condition:
IF A+B > C then A+B else 0

This formula work correclty in the table rows but not work in Grand Total .
May you help me to solved this issue?

Thanks in advance

Franco