Logical expression in a Query

Hi.

I have to build this relation in a query. I have two key figures F, S.

This is the logic:

If F=0 and S=0, then 0, If then IF F=0, S>0 THEN 100, IF F>0, S>0, THEN S/F

This is how I have built the syntax

(F=0 AND S=0)0+(F=0 AND S>0)100+(F>0 AND S>0)*(S/F)

The issue, when I use this expression here, only those values where F>0 AND S>0 show values. The rest of them show 'X' meaning infinite.

Suggestions please.

Cheers

Anand