50分求助

#include <bits/stdc++.h>
using namespace std;
int main(){
    long long n,sum_small=1,sum_all=1,a;
    cin >> n;
    for(int i =2;i<=n;i++){
        sum_small*=i;
        sum_all+=sum_small;
    }
    cout << sum_all;
    return 0;
}