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