** 这道题把我搞蒙了，求大佬指点！ **

#include <iostream>
using namespace std;
int main()
{
	long long n,sum = 0,x = 1;
	cin >> n;
	for (long long i = 1;i <= n;i++)
	{
		long long j = 1;
		while (j <= i)
		{
			x *= j;
			j += 1;
		}
		sum += x;
		x = 1;
	}
	cout << sum;
	return 0;
}