#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int n;
  cin >> n;
  long long int comb = 0, st = 1;
  while (st <= n) {
    comb++;
    comb += (n - st) * st;
    st++;
  }
  cout << comb << endl;
}
