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. Or you could say they're equal to 100%, either way. 100% and 1 are the same number. It's equal to 100%.