Greetings Excel Gurus,

I've searched the knowlege base for a formula to solve my issue, but have
found nothing.

Here's an illustration (where "A" is the column and numbers 1-6 downward are
rows):

A
1 <header
2 5
3 0
4 15
5 20
6 <formula

The formula in A6 would sum cells A4 and A5 (all values 0 between the
formula and first cell upward that contains a zero (wouldn't include cell
A2).

Thanks for your help!