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

fscanf(STDIN,'%d',$n);
$dll= new \splDoublyLinkedList();
for($i=0; $i<$n;$i++) {
  $line=trim(fgets(STDIN));
  if($line[0]==='i') {
    //先頭に要素を追加
    $dll->unshift(substr($line,7));
  } elseif($line[6]==='F') {
    //先頭からノードを取り出す
    $dll->shift();
  } elseif($line[6]==='L') {
    //末尾からノードを取り出す
    $dll->pop();
  }else{
    $check=substr($line, 7);
    foreach($dll as $key=>$val) {
      if($val === $check) {
        //指定したindexの値を削除する
        $dll->offsetUnset($key);
        break;
      }
    }
  }
}
$str = array();
while(true) {
  try{
    //先頭から取り出す
    $val = $dll->shift();
    $str[]=$val;
  }catch(Exception $e) {
    echo implode(' ',$str), PHP_EOL;
    break;
  }
}