# coding: utf-8

from __future__ import print_function
from __future__ import unicode_literals
from __future__ import division
from __future__ import absolute_import
import math
import string
import itertools
import fractions
import heapq
import collections
import re
import array
import bisect

def array2d(d1, d2, init = None):
    return [[init for _ in range(d2)] for _ in range(d1)]

def prod(n):
    r = 1
    for i in range(1, n + 1):
        r *= i
    return r

def combination(n, k):
    return prod(n) // prod(k) // prod(n-k)

def count(n, k):
    if n == 2 and k == 1:
        return 0
    if n == k:
        return 1
    if k != 1:
        cnt = 0
        for i in range(n - k + 1):
            cnt += combination(n-k, i)
        return cnt
    else:
        cnt = 0
        for i in range(1, n):
            cnt += count(n-1, i)
        return cnt

def main():
    N, K = map(int, input().split(" "))
    print(count(N, K))


if __name__ == "__main__":
    main()