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;
using System.Collections.Generic;

namespace AOJ.ALDS
{
    public class DoublyLinkedList
    {
        public static void Main()
        {
            int cmd_num = int.Parse(Console.ReadLine());

            var linked_list = new List<int>();
            for (int i = 0; i < cmd_num; i++)
            {
                string cmd_line = Console.ReadLine();
                string cmd;
                int key = 0;
                if (cmd_line.IndexOf(' ') > 0)
                {
                    var input = cmd_line.Split(' ');
                    cmd = input[0];
                    key = int.Parse(input[1]);
                }
                else { cmd = cmd_line; }

                switch (cmd)
                {
                    case "insert":
                        linked_list.Insert(0, key);
                        break;
                    case "delete":
                        if (linked_list.Exists(x => x == key))
                        {
                            int del_index = linked_list.Find(x => x == key);
                            linked_list.RemoveAt(del_index);
                        }
                        break;
                    case "deleteFirst":
                        linked_list.RemoveAt(0);
                        break;
                    case "deleteLast":
                        linked_list.RemoveAt(linked_list.Count - 1);
                        break;
                    default:
                        break;
                }
            }
            string output = "";
            linked_list.ForEach(x => output += x + " ");
            output = output.Trim();
            Console.WriteLine(output);
        }
    }
}