#include <iostream>
using namespace std;

int solve(int n,int n2) {
	int res=1;

	for (int i = 1; i <= n2; i++) {
		res *= n+1-i;
		res /= i;
	}

	return res;
}

int main()
{
	int n, k;
	
	cin >> n >> k;

	int ans = 0;

	if (k == 1) {
		for (int l = n - k - 2; l >= 0; l--) {
			for (int i = l; i >= 0; i--) {
				for (int j = 0; j <= i; j++) {
					ans += solve(i, j);
				}
			}
		}
	}
	else {
		for (int i = 0; i <= n - k; i++) {
			ans += solve(n - k, i);
		}
	}
	
	cout << ans << endl;

    return 0;
}