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: Wrong Answer)

class Node():
    def __init__(self,value,prv,nxt):
        self.value = value
        self.prv = prv
        self.nxt = nxt

class LinkedList():

    def __init__(self,head,tail):
        self.head = head
        self.tail = tail

    def insert(self,value):
        if self.head == None:
            self.head = Node(value,None,None)
            self.tail = self.head
        else:
            node = Node(value,None,self.head)
            if self.head.nxt == self.tail: #when only one node exists.
                self.head.prv = node
                self.head = node
            else:
                self.head.prv = node
                self.head = node

    def delete(self,value):
        check_node = self.head
        while not check_node == None:
            if check_node.value == value:
                if check_node == self.tail:
                    self.deleteLast()
                elif check_node == self.head:
                    self.head = check_node.nxt
                    check_node.nxt.prv = None
                else:
                    check_node.prv.nxt = check_node.nxt
                    check_node.nxt.prv = check_node.prv
                break
            check_node = check_node.nxt

    def deleteFirst(self):
        if self.head.nxt == None:
            self.head == None
        else:
            self.head = self.head.nxt

    def deleteLast(self):
        self.tail.prv.nxt = None
        self.tail = self.tail.prv

n = int(input())
linkedList = LinkedList(None,None)

def getAnswer(linkedList):
    answer = []
    check = linkedList.head
    while True:
        answer.append(check.value)
        if check.nxt == None:
            break
        else:
            check = check.nxt

    print(" ".join(map(str,answer)))

for _ in range(n):
    line = input()
    #print(line)
    if not line == "deleteFirst" and not line == "deleteLast":
        command = line.split(" ")[0]
        value = int(line.split(" ")[1])
    else:
        command = line

    if command == "insert":
        linkedList.insert(value)
    elif command == "delete":
        linkedList.delete(value)
    elif command == "deleteFirst":
        linkedList.deleteFirst()
    elif command == "deleteLast":
        linkedList.deleteLast()

    #getAnswer(linkedList)

getAnswer(linkedList)