#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base ::sync_with_stdio(false);
  int n;
  cin >> n;
  int pass = 0, ans = 0;
  while (n) {
    ans += n;
    ans += (pass * (n - 1));
    pass++;
    --n;
  }
  cout << ans;
  return 0;
}
