Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in C# (judge verdict: Wrong Answer)

using System;

namespace DoubleLinkedList
{
	class Node
	{
		public int value;
		public Node prev, post;

		public Node(int value) {
			this.value = value;
			this.prev = null;
			this.post = null;
		}

		public Node(int value, Node prev, Node post) {
			this.value = value;

			// ?????\?????????????????????????????\?¶??????±???????¨????
			this.prev = prev;
			this.post = post;
		}

		//
		// ??????????????§??????????????????
		//
		public void die() {
			prev.post = post;
			if (post != null)
				post.prev = prev;
		}

		public bool isFirst() {
			return this.prev == null;
		}

		public bool isLast() {
			return this.post == null;
		}

	}

	class DoublyLinkedList
	{
		Node root;

		public DoublyLinkedList() {
			root = new Node(-1, null, null);
		}

		//
		// ?????????????????????????´??????????
		//
		public void insert(int value) {
			if (root.post == null) {
				root.post = new Node (value, root, null);
			} else {
				Node node = new Node (value, root, root.post);
				if (root.post != null)
					root.post.prev = node;
				root.post = node;

			}
		}

		//
		// ??????????????????value???????????????????????????
		//
		public void delete(int value) {

			Node curNode = root.post;
			while (curNode != null) {
				if (curNode.value == value) {
					curNode.die ();
				}
				curNode = curNode.post;
			}

		}

		//
		// ???????????????????????????????????????
		//
		public void deleteFirst() {
			root.post.die();
		}

		//
		// ????????????????°????????´??????????
		//
		public void deleteLast() {
			Node curNode = root.post;
			while (!curNode.isLast ())
				curNode = curNode.post;
			curNode.die ();
		}

		//
		// ??????
		//
		public void dump() {
			Node curNode = root.post;
			int isf = 0;
			while (curNode != null) {
				if (isf++ > 0)
					Console.Write (" ");
				Console.Write (curNode.value); 
				curNode = curNode.post;
			}
			Console.WriteLine ();
		}

	}

	class MainClass
	{
		public static void Main (string[] args)
		{
			DoublyLinkedList list = new DoublyLinkedList ();

			int n = int.Parse (Console.ReadLine ());
			for (int i = 0; i < n; ++i) {
				string[] cmd = Console.ReadLine ().Split (' ');
				char[] cmd1 = cmd [0].ToCharArray ();

				// ????????????
				if (cmd1 [0] == 'i') {
					list.insert(int.Parse(cmd[1]));
				} else if (cmd1 [0] == 'd') {
					if (cmd1.Length > 6) {
						if (cmd1 [6] == 'F') {
							list.deleteFirst ();
						} else if (cmd1 [6] == 'L') {
							list.deleteLast ();
						}
					} else {
						list.delete (int.Parse (cmd [1]));
					}
				}
			}

			list.dump ();
		}
	}
}