Using formula to determine progress

[Zigi Fibert]

I'm want to track progress in a structure based on a project with a modified workflow.  I can't use the normal progress functionality as some of the statuses we create are not available in the dropdown of fields.  Instead I'm trying to use a formula:
if (
Status = "in Review" ; 25%
Status = "Reviewed" ; 50%
Status = "Start Implementation; 75%, 0%)

The formula doesn't resolve and the formula window just remain open.  

How can I fix that?

[Zigi Fibert]

I've updated it.  so now it reads:
if (

Status = "in Review" ; 25% ;

Status = "Reviewed" ; 50% ;

Status = "Start Implementation; 75%, 0%)

Still not working