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 Python (judge verdict: Time Limit Exceeded)

# http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_3_C
# Doubly Linked List
# Result: Time Limit Exceeded on test_case_10
import sys

class DoublyLikedList(object):
    def __init__(self):
        self.head = None
        self.tail = None

    def __str__(self):
        vals = []
        pointer = self.head
        while pointer != None:
            vals.append(str(pointer.val))
            pointer = pointer.next

        if len(vals) == 0:
            return ''
        else:
            return ' '.join(vals)

    def insert(self, x):
        itm = ListItem(x)
        if self.head == None:
            self.head = itm
            self.tail = itm
        else:
            itm.next = self.head
            self.head.prev = itm
            self.head = itm

    def delete(self, x):
        pointer = self.head
        while pointer != None:
            if pointer.val == x:
                if pointer == self.head:
                    self.delete_first()
                elif pointer == self.tail:
                    self.delete_last()
                else:
                    if pointer.prev != None:
                        pointer.prev.next = pointer.next
                    if pointer.next != None:
                        pointer.next.prev = pointer.prev
                break
            pointer = pointer.next

    def delete_first(self):
        if self.head == None:
            return
        self.head = self.head.next
        if self.head == None:
            self.tail = None
            return
        else:
            self.head.prev = None

    def delete_last(self):
        if self.tail == None:
            return
        if self.tail.prev == None:
            self.tail = None
            self.head = None
        else:
            self.tail = self.tail.prev
            self.tail.next = None

class ListItem(object):
    def __init__(self, x):
        self.val = x
        self.prev = None
        self.next = None

### main
lst = DoublyLikedList()
n = int(sys.stdin.readline().rstrip())
for e in range(0, n):
    strs = sys.stdin.readline().rstrip().split(' ')
    if strs[0] == 'insert':
        lst.insert(int(strs[1]))
    elif strs[0] == 'delete':
        lst.delete(int(strs[1]))
    elif strs[0] == 'deleteFirst':
        lst.delete_first()
    elif strs[0] == 'deleteLast':
        lst.delete_last()

print lst