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 Scala (judge verdict: Wrong Answer)

import scala.collection.mutable.ListBuffer
import scala.io.StdIn

object Main extends App {
  val n = StdIn.readInt()
  var list: ListBuffer[String] = ListBuffer()
  for (i <- 1 to n) {
    val o = StdIn.readLine().split(" ")
    list = o.head match {
      case "insert" => o.last +: list
      case "delete" => list - o.last
      case "deleteFirst" => list.tail
      case "deleteLast" => list - list.last
    }
  }
  println(list.mkString(" "))
}