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 Haskell (judge verdict: Memory Limit Exceeded)

import qualified Data.Vector         as V
import qualified Data.Vector.Mutable as VM
import Control.Applicative
import Control.Monad
import Data.IORef
import Text.Printf
import Data.List

type Cmd = [String]

doublyLinkedList :: [Cmd] -> [String]
doublyLinkedList cmds = loop [] cmds
  where
    loop xs [] = xs
    loop xs ((c : x) : cmd)
      | c == "insert" = seq xs $ loop ((head x) : xs) cmd
      | c == "delete" = seq xs $ loop (delete' (head x) xs) cmd
      | c == "deleteFirst" = seq xs $ loop (tail xs) cmd
      | c == "deleteLast"  = seq xs $ loop (init xs) cmd

    delete' _ [] = []
    delete' a (x : xs)
      | a == x = xs
      | otherwise = x : delete' a xs

main :: IO ()
main = do
  n  <- readLn
  xs <- map words <$> replicateM n getLine
  putStrLn $ unwords $ doublyLinkedList xs