题目P1009,返回结果：#1AC #2AC #3WA #4WA，

#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;

int main()
{
    int n;
    cin >> n;
    unsigned long long sum = 0;
    unsigned long long product;
    for (unsigned long long j = 1; j <= n; j++)
    {
        product = j;
        for (unsigned long long i = j - 1; i > 0; i--)
        {
            product *= i;
        }
        sum += product;
    }
    cout << sum << endl;
    return 0;
}