Imagine a hotel with an infinite number of rooms, numbered 1, 2, 3, and so on forever. All the rooms are full. A man comes in and asks the desk manager whether any rooms are available, and the desk manager replies, "All our rooms are full, but I’d be happy to accommodate you." How does he do it?
Go to Room 1 with a memo stating that management needs to move everyone. Memo should state that a person in room n is to relocate to room n+1 and to pass the memo to the person who was occupying room n+1. Room one will then become available and he can accommodate the newcomer.