Airplane around the world

You having infinite number of planes and infinite supply of fuel in a airport station. Now each airplane has a fuel capacity to allow it to fly exactly 1/2 way around the world, along a circle. 
The planes have the ability to refuel in flight. Though the fuel is unlimited, the island is the only source of fuel. What is the least number of aircraft necessary to get one plane all the way around the circle assuming that all of the aircraft must return safely to the airport?

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