As we all know, math is very important,so we must learn math well.

Alice and Bob are good friends.Today Alice ask Bob to help her judge whether a number is perfect or not. Perfect number is a kind of number like this:

First, 1 and 3 are perfect number.

Then if a and b are perfect numbers, 2+ab+2a+2b is also a perfect number.

For example, 1 and 3 are perfect numbers,  so 2+3+2+6 = 13 is perfect number.

If Bob can't help Alice,  Alice will be sad and Bob will be much more sad. So Bob must solve the problem to maintain their friendship. Can you help Bob to solve the problem?