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