Parking
The chief doctor of the hospital caught a cold and was unable to perform surgeries. Sitting in his office, he watched cars coming and going through the window. An ambulance arrived but couldn't park near the entrance, forcing the orderlies to carry the patient on a stretcher across the entire yard. "Chaos!" thought the chief doctor, and he called the staff programmer to investigate the parking process.
Consider the parking area divided into l equal sections along its length, with each ambulance needing exactly d consecutive sections to park. The choice of parking spot from all possible options is made with equal probability. Ambulance drivers are skilled at parking, so they can park even if the available space is exactly d. New vehicles continue to arrive as long as parking is feasible.
The task is to determine the expected number of parked vehicles to evaluate how much the parking area needs to be expanded.
Input
The input consists of one line with two natural numbers l (3 ≤ l ≤ 50) and d (3 ≤ d ≤ l).
Output
Output a single line with two integers separated by a "/" sign, without spaces, representing the expected number of parked vehicles as an irreducible fraction (even if the denominator is 1, it should still be displayed).