Each handshake is just really a selection of two of these people. And so we want to say how many ways can we select two people so that we have a different, each combination, each of these ways to select two people should have a different combination of people in it. If two of them had the same, if A, B, and B, A, these are the same combination. And so this is really a combinations problem. This is really equivalent to saying how many ways are there to choose two people from a pool of four, or four choose two, or four choose two. And so this is going to be, well, how many ways are there to permute four people into three spots, which is going to be four times three, which we just figured out right over there, which is 12. Actually, why don't I do it in that green color so you see where that came from.