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: Runtime Error)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace aizu1
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());

            DoublyList mylist = new DoublyList(n);

            for(int i=0;i<n;i++)
            {
                mylist.Parse(Console.ReadLine());
            }

            mylist.PrintAll();
        }
    }

    public struct DoublyList
    {
        LinkedList<int> list;
        private int n;

        public DoublyList(int n)
        {
            list = new LinkedList<int>();
            this.n = n;
        }
        public void insert(int x)
        {
            list.AddFirst(x);
        }

        public void delete(int x)
        {
            var index = list.Find(x);
            list.Remove(index);
        }

        public void deleteFirst()
        {
            list.RemoveFirst();
        }

        public void deleteLast()
        {
            list.RemoveLast();
        }

        public void Parse(string command)
        {
            if (command.Contains("insert")) insert(int.Parse(command.Split(' ')[1]));
            else if (command.Contains("deleteFirst")) deleteFirst();
            else if (command.Contains("deleteLast")) deleteLast();
            else delete(int.Parse(command.Split(' ')[1]));
        }

        public void PrintAll()
        {
            if (n == 0) Console.Write("");
            string s = "";
            for(int i=0;i<list.Count();i++)
            {
                s+=(list.ElementAt(i)+ ((i != (list.Count() - 1)) ?" ":"\n"));
            }
            Console.Write(s);
        }
    }
}