50 分……

#include <bits/stdc++.h>

using namespace std;
long long jc(int x) {

    long long ret = 1;
    for (int i = 1;i <= x; i++) {
        ret = ret * i;
    }
    return ret;
}
int main () {
    int n;
    cin >> n;

    int sum = 0;
    for (int i = 1;i <= n;i++) {
        long long ret1 = jc(i);

        sum +=  ret1;
    }
    printf("%d",sum);
    return 0;
}