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 C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Text;

namespace ALDS1_3_C {
    class Program {
        static void Main(string[] args) {
            int n = int.Parse(Console.ReadLine());
            LinkedList<int> ll = new LinkedList<int>();
            for(int i = 0; i < n; i++) {
                string[] input = Console.ReadLine().Split(' ');
                switch (input[0]) {
                    case "insert":
                        ll.AddFirst(int.Parse(input[1]));
                        break;
                    case "delete":
                        ll.Remove(int.Parse(input[1]));
                        break;
                    case "deleteFirst":
                        ll.RemoveFirst();
                        break;
                    case "deleteLast":
                        ll.RemoveLast();
                        break;
                }
            }

            StringBuilder sb = new StringBuilder();
            foreach (var num in ll) {
                sb.AppendFormat(" {0}", num);
            }
            Console.WriteLine(sb.ToString().TrimStart());
        }
    }
}