Planes Around the World Puzzle

The Puzzle:

Planes Around the World
You intend to fly non-stop around the world.

But you can only go halfway around the world on a full tank.

However you can arrange many planes exactly like yours to assist with refueling.

Assuming refueling can be done midair, ignoring refueling and turning time, and without crashing any plane, what is the minimum number of planes you will need?


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