Compiler Error On Linked List

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C#

I have written the following code on Linked List :

using System;
using System.Collections;
using System.Collections.Generic;
//using System.Collections.ObjectModel;
//using System.Text;

class MainClass
{
    static void Main()
    {
         LinkedList<int> list = new LinkedList<int>();
        
        list.AddFirst(10);
        list.AddLast(15);
        list.AddLast(3);
        list.AddLast(99);
        list.AddBefore(list.Last, 25);

        LinkedListNode<int> node = list.First;
        while (node != null)
        {
            Console.WriteLine(node.Value);
            node = node.Next;
        }
    }
}

Whenever I am tring to compile it I am getting the following error:

Error 1 The type or namespace name 'LinkedList' could not be found (are you missing a using directive or an assembly reference?)

Error 2 The type or namespace name 'LinkedList' could not be found (are you missing a using directive or an assembly reference?)

Error 3 The type or namespace name 'LinkedListNode' could not be found (are you missing a using directive or an assembly reference?)


NOTE: I am using Microsoft Visual C# 2008 Express Edition.