Find the last row in an Excel table column where value is not 0

Using an Excel formula, how can I find the last 'Period' in a table where the 'Contribution' is not 0?

Take the example table below. In this case I'm trying to make a formula that would find 'Period' 3.

I can use the INDEX function to fine the bottom row of the table, and thus give me 'Period'5, but I'm not sure how (or if it's possible) to amend the function to additionally check the 'Contribution' column.

=INDEX(MyTable[Period],ROWS(MyTable))