In problem A, we can solve it easier. We can calculate the number of group can be made of 2(s) and 1(s) = min(1, 2). And then plus with the remaining groups by 1s. We can get a sum like this = min(numberof1, numberof2) + (numberof1 — min(numberof1, numberof2))/3

oh, I didn't realize that. Can you send me some docs about that subject? tks btw