SSRS expression help

iif(Fields!Actded.Value <=0 ,0, iif(Fields!Actded.Value >0 and Fields!Actded.Value < 500001,Fields!Actuals.Value -Fields!Deductible.Value,500000))

The above expression is used in the detail section in a column. I want to add sum to this in the total section how can i ADD sum in this expression?

Any help ?

FM