#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> pl;

ll C[30][30];

void comb_table(ll N) {
	for (ll i = 0; i <= N; i++) {
		for (ll j = 0; j <= i; j++) {
			if (j == 0 || j == i) {
				C[i][j] = 1LL;
			}
			else {
				C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
			}
		}
	}
}

int main()
{
	int N, K;
	cin >> N >> K;

	comb_table(N);

	ll ans = 0;
	for (int i = 0; i <= N - K; i++) {
		ans += C[N - K][i];
	}
	cout << ans << endl;
	return	0;
}