Random Numbers

craps

I am generating random numbers between (1,12) okay and would like to do something like this:

Rule
Touch
CA - game.numbers to random (1,12)
CA - game.total to game.total + game.numbers

if - game.total is < 12
CA- game.numbers to random (1,12)

if - game.total is > 20 - STOP

(this is where I am getting lost - if the number is > 20 I do not want any more numbers generated

and need all of these actions to take place with just ONE touch of the actor not multiple touches - sort of automated.)