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