I'm trying to calculate (4, )

I used (s,a) = (1-s) I(s,a)

Am I right by saying (1-s) is undefined for s=4 and

I(4, 1/2) = 0 as s is a positive whole number

So (4, 1/2) =0

Am I doing this right or am I just making a mess of this

Thanks in advance