public class LinkedList {
 Item head;
 Item tail;

 public LinkedList() {
  head = null;
  tail = null;
 }

 // Add an item to the end of the list
 public void add(Item x) {
  if (tail == null) {
   tail = x;
   head = x;
  }
  else {
   tail.next = x;
   x.previous = tail;
   tail = x;
   x.next = null;
  }
 }

 // Remove the given item from the list
 public void remove(Item x) {
  if (x == head) {
   if (x == tail) {
    head = tail = null;
   }
   else {
    head = x.next;
    head.previous = null;
   }
  }
  else {
   if (x == tail) {
    tail = x.previous;
    tail.next = null;
   }
   else {
    x.previous.next = x.next;
    x.next.previous = x.previous;
   }
  }
 }

 // Return a string representation of the list
 public String toString() {
  if (head == null)
   return "[EMPTY]";

  String s = "[H:";
  Item currentItem = head;
  while (currentItem != null) {
   s += currentItem.data;
   if (currentItem != tail)
    s += "]<==>[";
   currentItem = currentItem.next;
  }
  return s + ":T]";
 }

 // add up the total data in the list
 public int totalData() {
  if (head == null)
   return 0;

  int  total = 0;
  Item currentItem = head;
  while (currentItem != null) {
   total += currentItem.data;
   currentItem = currentItem.next;
  }
  return total;
 }
}