using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(FormatNumber(1));

        Console.WriteLine(FormatNumber(11));

        Console.WriteLine(FormatNumber(111));

        Console.WriteLine(FormatNumber(1011));

        Console.WriteLine(FormatNumber(1100));

        Console.WriteLine(FormatNumber(1111));

        Console.WriteLine(FormatNumber(9900));

        Console.WriteLine(FormatNumber(10000));

        Console.WriteLine(FormatNumber(11211));

        Console.WriteLine(FormatNumber(112111));

        Console.WriteLine(FormatNumber(1001111));

        Console.WriteLine(FormatNumber(1111111));

        Console.WriteLine(FormatNumber(11010011));

        Console.WriteLine(FormatNumber(11111111));

        Console.WriteLine(FormatNumber(111111111));

        Console.WriteLine(FormatNumber(1111111111));

        Console.WriteLine(FormatNumber(Int32.MaxValue));

    }

    private static string FormatNumber(int num)

    {

            if (num < 1000)

            {

                return num.ToString();

            }

​

            if (num < 10000)

            {

                return (num / 1000.0).ToString("0.#k");

            }

​

            if (num < 1000000)

            {

                return (num / 1000.0).ToString("0.k");

            }

            if (num < 1000000000)

            {

                return (num / 1000000.0).ToString("0.M");

            }

​

            return (num / 1000000000.0).ToString("0.B");

    }

}