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;

class Program
{
    static void Main()
    {
        Queue<int> q = new Queue<int>();

        int c = int.Parse(Console.ReadLine());
        string[] s;
        int n = 0;

        for (int i = 0; i < c; i++)
        {
            s = Console.ReadLine().Split(' ');
            if (s.Length != 1) n = int.Parse(s[1]);

            if (s[0] == "insert")
                q.Enqueue(n);
            else if (s[0] == "delete")
                if (q.Count != 0) q = DeleteQueue(n, q);
            else if (s[0] == "deleteFirst")
                if (q.Count != 0) q = DeleteQueueFirst(q);
            else if (s[0] == "deleteLast")
                if (q.Count != 0) q.Dequeue();
        }

        string ret = "";

        while (0 < q.Count)
            ret = q.Dequeue() + " " + ret;
        Console.WriteLine(ret.TrimEnd());
    }

    static Queue<int> DeleteQueue(int idx, Queue<int> q)
    {
        Queue<int> r = new Queue<int>();
        int n;
        bool df = false;

        while (0 < q.Count)
        {
            n = q.Dequeue();

            if (!df && n == idx)
            {
                df = true;
                continue;
            }

            r.Enqueue(n);
        }

        return r;
    }

    static Queue<int> DeleteQueueFirst(Queue<int> q)
    {
        Queue<int> r = new Queue<int>();
        int n;

        while (1 < q.Count)
        {
            n = q.Dequeue();
            r.Enqueue(n);
        }

        return r;
    }
}