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: Wrong Answer)

# -*- coding: utf-8 -*-

n = input()
class DoubleLinkedList(object):
    def __init__(self):
        pass
        
    def insert(self, value):
        new = DoubleLinkedList()
        new.next = self.next
        new.prev = self
        self.next.prev = new
        self.next = new
        new.value = value
        
    def delete(self):
        next = self.next
        prev = self.prev
        self.next.prev = prev
        self.prev.next = next

head = DoubleLinkedList()
tail = DoubleLinkedList()
head.next = tail
tail.prev = head

for i in xrange(n):
    command = raw_input().split()
    if command[0] is "insert":
        head.insert(int(command[1]))
    elif command[0] is "delete":
        key = int(command[1])
        e = head.next
        while True:
            if e is tail:
                break
            if e.value is key:
                e.delete()
                break
            e = e.next
    elif command[0] is "deleteFirst":
        if not head.next is tail:
            head.next.delete()
    elif command[0] is "deleteLast":  
        if not tail.prev is head:
            tail.prev.delete()
    
e = head.next
while True:
    if e is tail:
        break
    print e.value,
    e = e.next