Help please.

I just got an nice answer on how to use the ".Formula()" function
programmatically but I forgot one detail: the range has to be
variable:

'ActiveWorkbook.Sheets("WSB").Cells(1, 2).Formula ="=COUNTIF('WSA'!
D2:D36000,""<N/A"")"

So, imagine that the range "D2:D36000" is dynamic. I've been trying
to substitute the value of "D36000" using "&d_end" but no success.
Something is telling me I should use a "range" type variable but I'm
too newbie I think.

Thanks.