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           Control.Applicative
import           Control.Monad
import           Control.Monad.State
import           Data.List

delete' :: Eq a => a -> [a] -> [a]
delete' _ [] = []
delete' n (x : xs) | n == x    = xs
                   | otherwise = x : delete' n xs

deleteFirst :: [a] -> [a]
deleteFirst []       = []
deleteFirst (x : xs) = xs

deleteLast :: [a] -> [a]
deleteLast = init

insert' :: a -> [a] -> [a]
insert' n xs = n : xs

parseLine :: String -> [String] -> [String]
parseLine str | str == "deleteFirst"  = deleteFirst
              | str == "deleteLast"   = deleteLast
              | head strs == "insert" = insert' (strs !! 1)
              | head strs == "delete" = delete' (strs !! 1)
  where strs = words str

doing :: Int -> [String] -> IO [String]
doing n xs = do
  f <- parseLine <$> getLine
  let r = f xs
  case n of
    1 -> return r
    _ -> doing (n - 1) r

main :: IO ()
main = do
  n <- readLn
  r <- doing n []
  putStrLn $ unwords r