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