#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <iomanip>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(int i = 0;i < n;++i)
long long dp[100][100] = {};
int main() {
	int n, k;
	cin >> n >> k;
	long long ans = 0;
	dp[0][k] = 1;
	for (int i = 1;i < n;++i) {
		long long now = 0;
		for (int q = 1;q <= n;++q) {
			dp[i][q] = now;
			now += dp[i - 1][q];
			if (q != 1) {
				ans += dp[i - 1][q];
			}
		}
	}
	cout << ans << endl;
}