文件目录

#include <iostream>
using namespace std;
int n, k;
long long f(int x, int num)
{
    if (x > num)
        return 0;
    if (x == 1)
        return 1;
    return x * f(x, num - 1) + f(x - 1, num - 1);
}
int main()
{
    cin >> n >> k;
    long long ans = f(k, n);
    cout << ans;
    return 0;
}