简简单单

#include <bits/stdc++.h>
using namespace std;

int n, m;

int main() {
    scanf("%d%d", &n, &m);
    int cnt = 0;
    int i = n, j = m;
    while (i > 0 && j > 0)
        cnt += i -- * j --;
    printf("%d\n", cnt);
}