Hippopotamus#4664
You think that your roof looks unpretty. So you opt for a new one, consisting of consecutive long narrow boards. You have two types of boards: wooden ones and iron ones, giving you an amazing total of 2^n possible roofs.
But the safety should not be left aside. Having considered the weight and the cruising speed of a falling hippopotamus, you decide to have at least iron boards among every consecutive boards.
How many possibilities do you have?
The input file contains three integers, , and , separated by spaces and/or line breaks. 1 \leq n \leq 60, 1 \leq m \leq 15, 0 \leq k \leq m \leq n.
Output the number of possibilities.
Example 1