So we're trying to figure out, this is what we're trying to figure out, the probability, I'll just call it the probability that someone shares. I'll call it the probability of sharing, probability of s. If this whole area is area 1 or area 100%, this green area right here, this is going to be 1 minus p of s. Or if we said that this is the probability, or another way we could say it, actually this is the best way to think about it. If this is different, so this is the probability of different birthdays. This is the probability that all 30 people have 30 different birthdays, right? No one shares with anyone. The probability that someone shares with someone else plus the probability that no one shares with anyone, they all have distinct birthdays, that's got to be equal to 1. Because we're either going to be in this situation or we're going to be in that situation.