#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    int sum = 0, factorial = 1;
    for (int i = 1; i <= n; ++i) {
        factorial *= i;
        sum += factorial;
    }
    cout << sum << endl;
    return 0;
}
/**************************************************************
	Problem: 1019
	User: admin
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/