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 PHP (judge verdict: Wrong Answer)

<?php

class Simulator
{
    public $queue = array();
    public $n_processes;
    public $quantum;

    public function __construct()
    {
        fscanf(STDIN, "%d", $this->n_processes);
        while ($this->n_processes > 0) {
            fscanf(STDIN, "%s %d", $operation, $key);
            $this->doOperation($operation, $key);
            $this->n_processes -= 1;
        }
    }

    public function doOperation($operation, $key)
    {
        switch ($operation) {
            case 'insert':
                array_unshift($this->queue, $key);
                break;
            case 'delete':
                if (array_search($key, $this->queue)) {
                    unset($this->queue[array_search($key, $this->queue)]);
                    array_values($this->queue);
                } else {
                    break;
                }
                break;
            case 'deleteFirst':
                unset($this->queue[0]);
                array_values($this->queue);
                break;
            case 'deleteLast':
                array_pop($this->queue);
                break;
        }
    }

    public function getAnswer()
    {
        // var_dump(array_values($this->queue));
        echo implode(' ', array_values($this->queue)) . "\n";
    }
}

$answer = new Simulator();
$answer->getAnswer();