A concierge in a ritzy hotel booked seven guests, even though
he had only 6 rooms available.
When the guests arrived, he did his best to make up for his mistake.
He took the first guest from the lobby and led him to the first
room. He asked the next guest to wait for few minutes in the first
room while he helped the others. Then he took the third one and
showed him to the second room. Next he led the fourth guest to
the third room, the fifth guest to the fourth room, and the sixth
guest to the fifth room. Then he returned to the first room, picked
up the seventh guest who was waiting for him there and led him
to the sixth room.
So, everything was fine, right?