#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  if (n < 4)
    cout << (n * (n - 1)) + 1;
  else if (n == 4)
    cout << ((n * 2) + ((n - 1) * 2));
  else {
    int sum = (n * 2) + ((n - 1) * 2);
    int count = n;
    int t = n - 4;
    int j = 2;
    for (int i = 0; i < t; i++) {
      count += j;
      sum += count;
      j++;
    }
    cout << sum;
  }
  return 0;
}
