#include <iostream>
using namespace std;

int f(int x)
{
    if (x <= 1) return 1;
    return x * f(x - 1);
}

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