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: Accepted)

using System;
using System.Collections.Generic;

class Program{
    public static void Main(){
        var n=int.Parse(Console.ReadLine());
        var lst=new LinkedList<int>();
        for(; n>0; n--){
            var s=Console.ReadLine().Split(' ');
            switch (s[0]) {
                case "insert":{
                    lst.AddFirst(int.Parse(s[1]));
                    break;
                }
                case "delete":{
                    lst.Remove(int.Parse(s[1]));
                    break;
                }
                case "deleteFirst":{
                    lst.RemoveFirst();
                    break;
                }
                case "deleteLast":{
                    lst.RemoveLast();
                    break;
                }
            }
        }

        while(true){
            Console.Write(lst.First.Value);
            lst.RemoveFirst();
            if(lst.Count>0){
                Console.Write(" ");
            } else{
                Console.WriteLine();
                break;
            }
        }
    }
}