def is_one(r, c):
if (r == c) or (c == 0):
return 1
return 0
N, K = map(int, input().split())
dp = [[is_one(i, j) for j in range(N)] for i in range(N)]
for i in range(2, N):
for j in range(1, i):
dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j]
print(dp[N - 1][K - 1])