using System;

using System.Collections.Generic;

public class Program

{

    static HashSet<string> set = new HashSet<string>();

    static List<string> list = new List<string>();

    static Dictionary<string, string> dict = new Dictionary<string, string>();

    public static void Main()

    {       

        for(int i = 0; i< 1000; i++)

        {

            for(int j = 1; j<100; j++)

            {

                AddItemToList("" + i + j);              

                AddItemToList("mandeep");

                AddItemToList("randeep");

                AddItemToList("mandeep");

                AddItemToList(null);

            }

        }       

        foreach(var item in set)

        {

            Console.WriteLine(item);

        }

        Console.WriteLine("Hello World");

    }

    private static void AddItemToList(string item)

    {

        //if(false == list.Contains(item))

        //{

            list.Add(item);

        //}

    }

    private static void AddItem(string item)

    {

        if(false == set.Contains(item))

        {

            set.Add(item);

        }

    }

}