Get The Value Of The Total Summary Of Crosstab In Crystal Report?

I got stuck with my program and I can't figure it out by myself. I have a problem in getting the total summary of my crosstab. Here's my sample report.As you can see on my report, you will notice that I set the Section Footer (it is not visible here) to Suppress (No Drill Down). Here's my formula

if {creditmemo_list.CreditReturn}="Yes" then
true
else
false

And it works fine. All I want is to get the value of total summary (Sum of @ii) of the crostab and subtract it to the value of #TotalBalance and the result would be the @GrandTotal.

The formula of my @GrandTotal should be #TotalBalance} - {(Sum of @ii)} <-Actual value of this object?+.`