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Solve the mystery of the XIII floor. I bet you can do it in just 5 steps using only 3 buttons.
User guide: You control the first elevator. The second elevator moves in sync, always maintaining the same floor distance. The building is ancient: if the load difference matches the larger elevator's capacity, the heavier one drops a floor.
Elevator rules:
If there are people on the floor, they enter the elevator up to its maximum capacity.
If the floor is empty, everyone exits the elevator.