public int numFives () {
    if (first == null) return 0;
    return numFivesH (first, 0);
  }
  private static int numFivesH (Node x, int result) {
    if (x.item == 5) result = result + 1;
    if (x.next != null) result = numFivesH (x.next, result);
    return result;
  }