#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm> 
#include<string>
#include<cstring>
using namespace std;
int main()
{
    int n;
    long long int a = 0;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        long long int sum = 1;
        for (int j = i; j >= 1; j--) {
            sum = sum * j;
        }
        a += sum;
    }
    cout << a << endl;
    return 0;
}