//DoublyLinkedList.java

class Node
{
    public int data;
    public Node next;
    public Node previous;

    public Node(int initialData)
    {
        data = initialData;
        next = null;
        previous = null;
    }
}

class LinkedList
{
    private Node head;
    private Node tail;

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

    public void append(Node newNode)
    {
        if (head == null)
        {
            head = newNode;
            tail = newNode;
        }
        else
        {
            tail.next = newNode;
            newNode.previous = tail;
            tail = newNode;
        }
    }

    public void prepend(Node newNode)
    {
        if (head == null)
        {
            head = newNode;
            tail = newNode;
        }
        else
        {
            newNode.next = head;
            head.previous = newNode;
            head = newNode;
        }
    }

    public void printList()
    {
        Node node = head;
        while (node != null)
        {
            System.out.print(node.data + " ");
            node = node.next;
        }
        System.out.println();
    }

    public void insertAfter
    (
        Node currentNode,
        Node newNode
    )
    {
        if (head == null)
        {
            head = newNode;
            tail = newNode;
        }
        else if (currentNode == tail)
        {
            tail.next = newNode;
            newNode.previous = tail;
            tail = newNode;
        }
        else
        {
            Node successor = currentNode.next;
            newNode.next = successor;
            newNode.previous = currentNode;
            currentNode.next = newNode;
            successor.previous = newNode;
        }
    }

    public void remove(Node currentNode)
    {
        Node successor = currentNode.next;
        Node predecessor = currentNode.previous;

        if (successor != null)
            successor.previous = predecessor;

        if (predecessor != null)
            predecessor.next = successor;

        if (currentNode == head)
            head = successor;

        if (currentNode == tail)
            tail = predecessor;
    }
}