#include<iostream>
using namespace std;
int S(long long n)
{
	if (n != 1)return n*S(n - 1);
	else return 1;
}
int main()
{
	int n;
	cin >> n;
	int sum = 0;
	for (int i = 1; i <= n; i++)
	{
		sum += S(i);
	}
	cout << sum << endl;
}