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)

import sys

class Node:
	def __init__(self, value):
		self.value = value
		self.prev = None
		self.next = None

class DoublyLinkedList:
	def __init__(self):
		self.head = None
		self.tail = None
		self.size = 0

	def get_size(self):
		return self.size

	def is_empty(self):
		return self.size == 0

	def insert(self, value):
		node = Node(value)
		if self.is_empty():
			self.head = self.tail = node
		else:
			self.head.prev = node
			node.next = self.head
			self.head = node
		self.size += 1

	def deleteFirst(self):
		if self.is_empty():
			return
		if self.size == 1:
			self.head = self.tail = None
		else:
			self.head = self.head.next
			self.head.prev = None
		self.size -= 1
	
	def deleteLast(self):
		if self.is_empty():
			return
		if self.size == 1:
			self.head = self.tail = None
		else:
			self.tail = self.tail.prev
			self.tail.next = None
		self.size -= 1

	def delete(self, value):
		if self.is_empty():
			return
		if self.head.value == value:
			self.deleteFirst()
		else:
			node1 = self.head.next
			node2 = self.tail
			node3 = None
			while node1 != None:
				if node1.value == value:
					prev = node1.prev
					next = node1.next
					prev.next = next
					if next != None:
						next.prev = prev
					else:
						self.tail = prev
					self.size -= 1
					break
				elif node1 == node2:
					if node3 == None:
						break;
					else:
						node1 = node3
				else:
					node1 = node1.next
					if node2.value == value:
						node3 = node2
					node2 = node2.prev
		return

	def print(self):
		node = self.head
		while node != None:
			sys.stdout.write(str(node.value))
			node = node.next
			if node != None:
				sys.stdout.write(' ')
		print()

n = int(input())
dll = DoublyLinkedList()
for n in range(n):
	cmd = sys.stdin.readline().strip().split()
	if cmd[0] == 'deleteFirst':
		dll.deleteFirst()
	elif cmd[0] == 'deleteLast':
		dll.deleteLast()
	else:
		if cmd[0] == 'insert':
			dll.insert(int(cmd[1]))
		else:
			dll.delete(int(cmd[1]))
dll.print()