#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;
}