#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  scanf("%d", &n);
  int iterations = 1;
  int sum = n;
  while (n != 1) {
    sum += (n - 1) + iterations * (n - 2);
    n--;
    iterations++;
  }
  printf("%d\n", sum);
  return 0;
}
