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