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