#include <bits/stdc++.h>
int main(void) {
  int n;
  scanf("%d", &n);
  int k = 0;
  for (int i = n; i >= 1; i--) {
    for (int j = 1; j < i; j++) k += (n - i + 1);
    k++;
  }
  printf("%d\n", k);
  return 0;
}
