#include <bits/stdc++.h>
int cmp(const void *a, const void *b) { return *(int *)a - *(int *)b; }
int main(void) {
  int n = 0;
  scanf("%d", &n);
  int total = 1;
  for (int i = 1; i <= n; ++i) {
    for (int x = 1; x <= n - i; ++x) {
      total += i;
    }
  }
  total += n - 1;
  printf("%d\n", total);
  return 0;
}
