#include <bits/stdc++.h>
using namespace std;
const int Max = 2e6 + 10;
const int Mod = 1e9 + 7;
bool compare(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.first > b.first);
}
int main() {
  (ios_base::sync_with_stdio(false), cin.tie(NULL));
  ;
  int n, i, j, ans = 0;
  cin >> n;
  for (i = 1; i <= n; i++) ans += i * (n - i);
  cout << ans + n << endl;
}
