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 MyDLList:
    head = tail = None
    size = 0

    def append_left(self, elm):
        if self.is_empty():
            self.head = self.tail = [elm, None, None]
            # elm, prev, next
        else:
            cur = [elm, None, self.head]
            self.head[1] = cur
            self.head = cur
        self.size += 1

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

    def list_search(self, elm):
        cur = self.head
        i = 1
        while i < self.size and cur[0] != elm:
            cur = cur[2]
            i += 1
        if cur != elm:
            cur = None
        return cur

    def delete(self, elm):
        cur = self.list_search(elm)
        if cur:
            if cur == self.head:
                deleted = self.delete_first()
            elif cur == self.tail:
                deleted = self.delete_last()
            else:
                deleted = cur[0]
                cur[1][2] = cur[2]
                cur[2][1] = cur[1]
                self.size -= 1
        else:
            deleted = None
        return deleted

    def delete_first(self):
        cur = self.head
        self.head[2][1] = None
        self.head = self.head[2]
        self.size -= 1
        return cur[0]

    def delete_last(self):
        cur = self.tail
        self.tail[1][2] = None
        self.tail = self.tail[1]
        self.size -= 1
        return cur[0]

    def __str__(self):
        cur = self.head
        result = ""
        while cur != self.tail:
            result += cur[0] + " "
            cur = cur[2]
        result += cur[0]
        return result

n = int(input())

dl = MyDLList()


for i in range(n):
    x = list(map(str, input().split()))
    if x[0] == "insert":
        dl.append_left(x[1])
    elif x[0] == "delete":
        dl.delete(x[1])
    elif x[0] == "deleteFirst":
        dl.delete_first()
    elif x[0] == "deleteLast":
        dl.delete_last()

print(dl)