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: Runtime Error)

# coding:utf-8
# Doubly Linked List

class DLL:

    def __init__(self):
        self.array = []

    def insert(self, x):
        self.array = [x] + self.array
    
    def delete(self, x):
        del self.array[self.array.index(x)]

    def deleteFirst(self):
        del self.array[0]

    def deleteLast(self):
        del self.array[len(self.array)-1]


def main():

    dll = DLL()
    n = int(input())
    ans = ""

    for _ in range(n):
        operation = input().split()
        command = operation[0]
        if command in ["insert", "delete"]:
            key = operation[1]
            eval("dll." + command + '(' + key + ')')

        else:
            eval("dll." + command + "()")

    for value in dll.array:
        ans += str(value) + " "

    print(ans.rstrip())

if __name__ == "__main__":
    main()