#include <bits/stdc++.h>
using namespace std;
long long n, s;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  for (int i = 0; i < n; ++i) s += (n - i) * (i) + 1;
  cout << s;
}
