#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, l, h, min = 0, max = 0, m = 0, k;
  cin >> n;
  l = n;
  for (long long int i = n; i > 1; i--) {
    l = l + (i - 1) + (i - 2) * (n - 1 - (i - 2));
  }
  cout << l;
}
