#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int s = n;
  int a = 2, p = 0;
  while (n--) {
    if (n >= 1) p = p + a * (n - 1) + 1;
    a++;
  }
  cout << p + s;
}
