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