#include <iostream>

using namespace std;


int main()
{
    int num;
    cin >> num;
    int sum = 0;
    for (int i = 1; i <= num; i++) {
        int mul = 1;
        for (int j = i; j >= 1; j--) {
            mul = mul * j;
        }
        sum += mul;
    }
    cout << sum;
    return 0;
}