// yukicoder: No.411 昇順昇順ソート
// 2019.6.23 bal4u

#include <stdio.h>

int dp[22][22];

int main()
{
	int i, j, k, f, K, N, ans;
	
	scanf("%d%d", &N, &K);
	dp[1][K] = 1;
	ans = (K != 1);
	for (i = 2 ; i <= N; i++) {
		f = 0;
		for (j = K; j < N; j++) if (dp[i-1][j]) {
			f = 1;
			for (k = j+1; k <= N; k++) dp[i][k] += dp[i-1][j];
		}
		if (!f) break;
		for (k = K+1; k <= N; k++) if (k != i) ans += dp[i][k];
	}
	printf("%d\n", ans);
	return 0;
}