#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  int n;
  scanf("%d", &n);
  ll ans = 0;
  for (int i = 0; i < n; i++) {
    ll pressed = i;
    ll wrong_button = (n - i - 1);
    ll right_button = 1;
    ans += (wrong_button * pressed);
    ans += (wrong_button + right_button);
  }
  printf("%lld\n", ans);
}
