#include <bits/stdc++.h>
using namespace std;
int main() {
  long long a, b, c, d, e;
  cin >> a;
  long long p[2222];
  p[0] = 1;
  d = 1;
  for (int i = 1; i < a; i++) {
    p[i] = i + p[i - 1];
    d = d + p[i];
  }
  cout << d;
}
