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: Time Limit Exceeded)

<?php

fscanf(STDIN, '%d', $n);
$list = new SplDoublyLinkedList();
for ($i = 0; $i < $n; $i++) {
    fscanf(STDIN, '%s %d', $cmd, $x);
    switch ($cmd) {
        case 'insert':
            $list->unshift($x);
            break;
        case 'delete':
            foreach ($list as $key => $val) {
                if ($val === $x) {
                    $list->offsetUnset($key);
                    break;
                }
            }
            break;
        case 'deleteFirst':
            $list->offsetUnset(0);
            break;
        case 'deleteLast':
            $list->offsetUnset($list->count() - 1);
            break;
        default:
            throw new Error('error');
    }
}

$str = array();
foreach ($list as $val) {
    $str[] = $val;
}
echo implode(' ', $str), PHP_EOL;