#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int main() {
  long long n;
  cin >> n;
  long long ans = n;
  for (long long i = 1; i < n; ++i) ans += (n - i) * i;
  cout << ans << endl;
  return 0;
}
