The operator >= is a boolean operator, it tests what the values on either side of the operator are, and then decides if the left value is larger than , or equal to the value on the right side, the result can be only one of two possible outcomes:
1: the left value is larger than or equal to the right value.
0: The left value is less than the right value.
So the result is either 1, or 0, for 'true' or 'false'.
That is why you get an s_k value of 0.
To do what you want, you have to use an if statement, and that involves a 'condition' for which you can use a boolean operator like >=.
The if statement goes like this:
if('condition','value if true', 'value if false')
an example:
result:=if(a>=3,1,2)
If a>=3, then result becomes 1, if, not, result becomes 2.
I'm sure you can apply this to your problem. If you need further help, be sure to attach your Prime worksheet, that saves typing (and errors that may come with that) for those who want to help you.
Success!
Luc