#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int sum = n, sum2 = 0;
  int b = n;
  for (int i = 1; i < b; i++) {
    sum2 += (n - 1) * i;
    n--;
  }
  cout << sum + sum2;
  return 0;
}
