#include<iostream>
#include<algorithm>

using namespace std;

typedef long long LL;

LL cal(int x) {
	if (x == 1) return x;
	return x * cal(x - 1);
}

int main() {
	
	int n;
	cin >> n;
	
	LL sum  = 0;
	for (int i = 1; i <= n; i ++ )
		sum += cal(i);
	
	cout << sum << endl;
	
	return 0;
}