#!usr/bin/env python
# -*- coding:utf-8 -*-

def ascend(N,K):
    num = 0
    if N == 1:
        return 0
    if N == K:
        return 1
    else:
        for i in range(K, N):
            num = num + ascend(N-1,i)
        if K == 1:
            return num
        else:
            return num+1
    
if __name__ == '__main__':
    S = raw_input().split()
    N = int(S[0])
    K = int(S[1])

    num = ascend(N,K)
    print num
    print '\n'