#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  long long int s = n + 1;
  for (int i = 2; i < n; i++) s = s + ((n - i) * i + 1);
  if (n != 1)
    cout << s;
  else
    cout << s - 1;
}
