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: Time Limit Exceeded)

import Data.List.Split
import Data.List
import Control.Monad

main = do
    a <- getContents
    let aa = splitOn "\n" a
    let b = tail $ init aa

    -- foldl' (+) 0 [1,2,3] => 6
    let aaa = foldl' od [] b
    let bbb = map (\x -> if x == -1 then "" else (show x)++ " ") aaa

    putStrLn $ init $ concat bbb
    return ()

od l s = me l o v
    where
        --(o:v1) = splitOn " " s
        (o:v1) = splitOn " " s
        vvv = if (length v1) == 0 then "-1" else head v1
        v = read vvv :: Int

me :: [Int] -> String -> Int -> [Int]
me l "insert" b      = [b] ++ l
--me l "delete" b      = concatMap (\x -> if x == b then [] else [x]) l
me l "delete" b      = delfst [] l b
me l "deleteFirst" b = tail l
me l "deleteLast" b  = init l

delfst lt [] v = lt
delfst lt (x: xs) v = if x == v then lt ++ xs else delfst (lt ++ [x]) xs v