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: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace _20180305_AOJ
{
    class ALDS1_3C
    {
        static void Main(string[] args)
        {
            for (;;)
            {
                string line = Console.ReadLine();
                if (string.IsNullOrEmpty(line))
                {
                    break;
                }

                List<string> list = new List<string>();
                int n = int.Parse(line);
                for (int i = 0; i < n; i++)
                {
                    string[] command = Console.ReadLine().Split(' ');
                    if (command.Length > 1)
                    {
                        string val = command[1];
                        switch (command[0])
                        {
                            case "insert":
                                list.Insert(0, val);
                                break;
                            case "delete":
                                list.Remove(val);
                                break;
                        }
                    }
                    else
                    {
                        switch (command[0])
                        {
                            case "deleteFirst":
                                list.RemoveAt(0);
                                break;
                            case "deleteLast":
                                list.RemoveAt(list.Count - 1);
                                break;
                        }
                    }
                }

                for (int i = 0; i < list.Count - 1; i++)
                {
                    Console.Write(string.Format("{0} ", list[i]));
                }
                Console.WriteLine(list[list.Count - 1]);
            }
        }
    }
}