#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int t = n;
  int sum = 0;
  int p = 0;
  for (int i = 0; i < n - 1; i++) {
    sum += (n - p) + (p) * (n - p - 1);
    p++;
  }
  cout << sum + 1;
}
