#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long k = 2, n, s = 0, p = 1;
  cin >> n;
  p = n - 2;
  s = n + n - 1;
  while ((k < n) && (p < n)) {
    s += (k * p);
    k++;
    p--;
  }
  cout << s << endl;
  return 0;
}
