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;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;



namespace free
{
    class Node
    {
        public int value;
        public Node next, prev;
        public Node(int _value, Node _next, Node _prev)
        {
            value = _value;
            next = _next;
            prev = _prev;
        }
    }

    class DL
    {
        public Node last, head;
        public int cnt; 
        public DL()
        {
            last = new Node(-1, null, null);
            head = new Node(-2, null, null);
            last.next = head;
            head.prev = last;
            cnt = 0;
        }
        public void Insert(int value)
        {
            Node newNode = new Node(value, head, head.prev);
            head.prev.next = newNode;
            head.prev = newNode;
            cnt++;
        }
        public void DeleteLast()
        {
            if (cnt == 0) return;
            Node target = last.next;
            last.next = target.next;
            target.next.prev = last;
            cnt--;
        }
        public void DeleteFirst()
        {
            if (cnt == 0) return;
            Node target = head.prev;
            head.prev = target.prev;
            target.prev.next = head;
            cnt--;
        }
        public void Delete(int value)
        {
            Node p = head.prev;
            while (p.value != -1)
            {
                if (p.value != value)
                {
                    p = p.prev;
                    continue;
                }
                p.prev.next = p.next;
                p.next.prev = p.prev;
                cnt--;
                break;
            }
        }
        public void Show()
        {
            Node p = head.prev;
            bool addSpace = false;
            while(p.value != -1)
            {
                if (!addSpace) addSpace = true;
                else Console.Write(" ");
                
                Console.Write("{0}",p.value);
                p = p.prev;
            }
            Console.WriteLine();
        }
    }

    class Program4
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            var dl = new DL();
            
            for (int i = 0; i < n; i++)
            {
                string[] line = Console.ReadLine().Split(' ');
                if (line[0] == "insert")
                {
                    dl.Insert(int.Parse(line[1]));
                }
                else if (line[0] == "deleteFirst")
                {
                    dl.DeleteFirst();
                }
                else if (line[0] == "deleteLast")
                {
                    dl.DeleteLast();
                }
                else
                {
                    dl.Delete(int.Parse(line[1]));
                }
            }

            dl.Show();
        }
    }
}