using System;

using System.Collections;

public class Program

{

    public static void Main()

    {

        ArrayList phoneBook = new ArrayList();

        phoneBook.Add(new ArrayList() {"Andre", "9999-0001"});

        phoneBook.Add(new ArrayList() {"Bruno", "9999-0002"});

        phoneBook.Add(new ArrayList() {"Carlos", "9999-0003"});

        phoneBook.Add(new ArrayList() {"Diego", "9999-0004"});

        phoneBook.Add(new ArrayList() {"Eli", "9999-0005"});

        phoneBook.Add(new ArrayList() {"Fabio", "9999-0006"});

        phoneBook.Add(new ArrayList() {"Gustavo", "9999-0007"});

        phoneBook.Add(new ArrayList() {"Honorio", "9999-0008"});

        phoneBook.Add(new ArrayList() {"Igor", "9999-0009"});

        phoneBook.Add(new ArrayList() {"Joao", "9999-0010"});

        phoneBook.Add(new ArrayList() {"Kaio", "9999-0011"});

        phoneBook.Add(new ArrayList() {"Luan", "9999-0012"});

        phoneBook.Add(new ArrayList() {"Manoel", "9999-0013"});

        phoneBook.Add(new ArrayList() {"Natan", "9999-0014"});

        phoneBook.Add(new ArrayList() {"Oto", "9999-0015"});

        phoneBook.Add(new ArrayList() {"Paulo", "9999-0016"});

        phoneBook.Add(new ArrayList() {"Quevis", "9999-0017"});

        phoneBook.Add(new ArrayList() {"Ramon", "9999-0018"});

        phoneBook.Add(new ArrayList() {"Samuel", "9999-0019"});

        phoneBook.Add(new ArrayList() {"Tiago", "9999-0020"});

        phoneBook.Add(new ArrayList() {"Ubaldo", "9999-0021"});

        phoneBook.Add(new ArrayList() {"Victor", "9999-0022"});

        phoneBook.Add(new ArrayList() {"Wingler", "9999-0023"});

        phoneBook.Add(new ArrayList() {"Xavier", "9999-0024"});

        phoneBook.Add(new ArrayList() {"Yan", "9999-0025"});

        phoneBook.Add(new ArrayList() {"Zarate", "9999-0026"});

        Console.WriteLine(checkNumber(phoneBook, "Xavier"));

    }

    public static string checkNumber(ArrayList phoneBook, String name) 

    {

        ArrayList contact = new ArrayList();

        while (phoneBook.Count > 1)

        {

            int middlePos = phoneBook.Count/2;

            contact = (ArrayList)phoneBook[middlePos];

​

            if (string.Compare(name, (string)contact[0]) == 1)

            {

                phoneBook = phoneBook.GetRange(middlePos+1, phoneBook.Count - middlePos -1);

            }

            else if (string.Compare(name, (string)contact[0]) == -1)

            {

                phoneBook = phoneBook.GetRange(0, phoneBook.Count - middlePos);

            }

            else if (string.Compare((string)contact[0], name) == 0)

            {

                return (string)contact[1];

            }

        }

        if (phoneBook.Count == 1)

        {

            contact = (ArrayList)phoneBook[0];

            return string.Compare((string)contact[0], name) == 0 ? (string)contact[1] : "Not Found";

        }

        return "Not Found";

    }

}