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 Python3 (judge verdict: Time Limit Exceeded)

class Node:
    def __init__(self, key, prevNode, nextNode):
        self.key = key
        self.prevNode = prevNode
        self.nextNode = nextNode

def deleteNode(node):
    if node == fNode:
        return
    node.prevNode.nextNode = node.nextNode
    node.nextNode.prevNode = node.prevNode

def searchNode(key):
    global fNode
    node = fNode.nextNode
    while node != fNode and node.key != key:
        node = node.nextNode
    return node

'''
def searchLast():
    global fNode
    node = fNode.nextNode
    while node != fNode:
        prevNode = node
        node = node.nextNode
    return prevNode
'''

def nodeList():
    global fNode
    node = fNode.nextNode
    keys = []
    while node != fNode:
        keys.append(node.key)
        node = node.nextNode

    print(" ".join(keys))

# ????????????????????????
fNode = Node(None, None, None)
fNode.prevNode = fNode
fNode.nextNode = fNode

n = int(input())

for i in range(0, n):
    inputs = input().split(' ')
    command = inputs[0]

    if command == 'insert':
        insertNode = Node(inputs[1], fNode, fNode.nextNode)
        fNode.nextNode.prevNode = insertNode
        fNode.nextNode = insertNode
    if command == 'delete':
        deleteNode(searchNode(inputs[1]))
    if command == 'deleteFirst':
        deleteNode(fNode.nextNode)
    if command == 'deleteLast':
        deleteNode(fNode.prevNode)
        #deleteNode(searchLast())
nodeList()