#include <bits/stdc++.h>
int main() {
  int c;
  scanf("%d", &c);
  int t1 = 1, t2 = c - 1;
  long int n = 0;
  while (1) {
    if (t2 == 0) break;
    n += (t1 * t2 + 1);
    t1++;
    t2--;
  }
  printf("%ld\n", n + 1);
}
