So you need to shake the hand exactly once of every other person in the room so that you all meet. So my question to you is, if each of these people need to shake the hand of every other person exactly once, how many handshakes are going to occur? The number of handshakes that are going to occur. So like always, pause the video and see if you can make sense of this. All right, I'm assuming you've had a go at it. So one way to think about it is, okay, if you say there's a handshake, well, a handshake has two people are party to a handshake. We're not talking about some new three-person handshake or four-person handshake.