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 Ruby (judge verdict: Time Limit Exceeded)


def execute_process(orders) #orders???????¬??????????
  list = []
  length = orders.length
  for i in 0..(length-1)
    if orders[i][0] == "insert"
      list.unshift(orders[i][1].to_i)
    elsif  orders[i][0] == "delete"
      first_order_number = list.index(orders[i][1].to_i)
      if first_order_number == nil
        next
      else
        list.delete_at(first_order_number)
      end
    elsif orders[i][0] == "deleteFirst"
      list.delete_at(0)
    elsif orders[i][0] == "deleteLast"
      list.delete_at(-1)
    else
      puts "error!"
    end
  end
  return list
end


n = gets.chomp.to_i
orders = []
n.times do
  order = gets.chomp.split
  orders.push(order)
end

output = execute_process(orders)
puts output.join(' ')