n = 12;
While[n > 0,
 c = ChoiceDialog["Current amount = " <> ToString[n] <> "\nHow many do you want to pick?", {1 -> 1, 2 -> 2, 3 -> 3}];
 n -= c;
 ChoiceDialog["Current amount = " <> ToString[n] <> "\nComputer takes " <> ToString[4 - c]];
 n -= (4 - c);
 ]
ChoiceDialog["Current amount = " <> ToString[n] <> "\n You lost!"]