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: Accepted)

<?php

class Operator
{
    private $linked_list;
    private $operations_count;

    public function doOperations()
    {
        fscanf(STDIN, '%d', $this->operations_count);
        $this->linked_list = new \SplDoublyLinkedList();
        for (;$this->operations_count > 0;$this->operations_count -= 1) {
            $operation = explode(' ', trim(fgets(STDIN)));
            if ($operation[0] === 'insert') {
                $this->linked_list->unshift($operation[1]);
            } elseif ($operation[0] === 'deleteFirst') {
                $this->linked_list->shift();
            } elseif ($operation[0] === 'deleteLast') {
                $this->linked_list->pop();
            } elseif ($operation[0] === 'delete') {
                foreach ($this->linked_list as $key => $element) {
                    if ($element === $operation[1]) {
                        $this->linked_list->offsetUnset($key);
                        break;
                    }
                }
            }
        }
    }

    public function getAnswer()
    {
        $keys_operated = array();

        while (count($this->linked_list) > 0) {
            $keys_operated[] = $this->linked_list->shift();
        }
        echo implode(' ', $keys_operated), PHP_EOL;
    }
}

$operator = new Operator();
$operator->doOperations();
$operator->getAnswer();