A fleet of planes each have the fuel capacity to travel 100 miles before landing or running out of fuel. The planes are all parked at an airfield on the edge of a 200-mile wide ocean. Every plane has the ability to transfer fuel to other planes in mid-air, or to refuel completely by returning to the airfield. One of the planes carries an important dignitary who need to travel to the other side of the ocean. What is the minimum number of planes that can be used to accomplish this, without any plane crashing?