#include <bits/stdc++.h>
using namespace std;
int main() {
  int num, sum = 0, counter = 1, sum1 = 0;
  int tap;
  cin >> num;
  if (num == 1) {
    sum += num;
  }
  for (int i = 0; i < (num - 1); i++) {
    if (i == 0) {
      sum1 = (num + 1);
      sum += sum1;
    } else {
      sum1 = (i + 1) * (num - (i + 1)) + 1;
      sum += sum1;
    }
  }
  cout << sum;
  return 0;
}
