Can anybody provide some code for the following ..

Basically, the user is playing a game which consists of 21 rounds - after
the first 4 rounds they are forced to 'gamble' (and taken sheet4) after the
next 3 and every 3 thereafter they are again forced to 'gamble' until there
are just two rounds left. At this point the game ends and sheet6 is opened

So what I really need is a 'counter' which starts at 21 and each time the
user clciks a cell on sheet1 the counter reduces by 1. When this counter
reaches either 18,15,11,8,4,2 it firstly reduces the counter by 1 then runs
the 'banker' macro.

I hope I have explained this well and hope even more it can be done!
many thanks in advance