On an Island, there is an airport that has an unlimited number of identical air-planes. Each air-plane has a fuel capacity to allow it to fly exactly 1/2 way around the world, along a great circle. The planes have the ability to refuel in flight without loss of speed or spillage of fuel. Though the fuel is unlimited, the island is the only source of fuel. You can ignore the time and fuel consumption of refueling.
What is the minimum number of air-planes required to get one airplane all the way around the world assuming that all of the airplanes must return safely to the airport?
The Answer is an integer. Just put the number without any decimal places.