#include <bits/stdc++.h>

using namespace std;
typedef long long LL;


//求组合数的优化后办法
//优点：从1开始除和乘，可以防止过早溢出和除法除不尽
LL C(int n, int m) {
    LL sum = 1;
    for (int i = 1; i <= m; i++)
        sum = sum * (n - m + i) / i;
    return sum;
}

int main() {
    int n = 10, m = 4;
    //组合公式法
    cout << C(n, m) << endl;
    return 0;
}