计算阶乘和

题源

团体程序设计天梯赛

题解

#include<iostream>
using namespace std;
int N,an = 1,sum = 0;
int main(){
    cin >> N;
    for(int i = 1;i <= N;i++){
        an *= i;
        sum += an;
    }
    cout << sum << endl;
    return 0;
}