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)

import sys
res = dict()
dll = [None] * 2000000
left = 0
right = 0
n = int(input())
for inpt in sys.stdin.read().splitlines():
    i = inpt.split()
    if i[0] == "insert":
        x = int(i[1])
        dll[left] = x
        if(x in res):
            res[x].append(left)
        else:
            res[x] = [left]
        left += 1
    if i[0] == "delete":
        x = int(i[1])
        if(x in res):
            ind = max(res[x])
            dll[ind] = None
            res[x].remove(ind)
            if(len(res[x]) == 0):
                del res[x]
            if(ind == (left - 1)):
                left = ind
            if(ind == right):
                right += 1
    if i[0] == "deleteFirst":
        left -= 1
        dll[left] = None
    if i[0] == "deleteLast":
        right += 1
    # print(dll[right:left])
ret = []
for x in dll[right:left]:
    if(x is not None):
        ret.append(str(x))
ret.reverse()
print(" ".join(ret))