# subs6-q12
# Section 6, Q.12, p.24, p.250
# inputs: 5 2

def c(n, s):
  if (s == 0) or (n == s):
    return 1
  else:
    return c(n-1, s-1) + c(n-1, s)

n, s = map(int, input("n s=? ").split())
print(c(n, s))