#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(NULL);
  cin.tie(NULL);
  cout.tie(NULL);
  int n, t = 0;
  cin >> n;
  if (n == 1) {
    cout << "1";
    return 0;
  }
  for (int i = 2; i < n; i++) t += 1 + i * (n - i);
  cout << t + n + 1;
  return 0;
}
