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