using System;

public class Program

{

    public static void Main()

    {

            string LS = "";

            string CS = "";

​

            while (true)

            {

​

                Console.Write("enter small letter");

                char x = Console.ReadKey().KeyChar;

                Console.WriteLine();

                if (x == '$')

                {

                    break;

                }

                if (x >= 'a' && x <= 'z')

                {

​

                    if (x == 'a' || x == 'k')

                    {

                        CS += x;

                    }

                    else

                    {

                        if (CS.Length > LS.Length)

                        {

                            LS = CS;

                        }

                        CS = "";

                    }

                }

                else

                {

                    Console.WriteLine("the letter is not small");

                    break;

                }

            }

​

            if (CS.Length > LS.Length)

            {

                    LS = CS;

            }

            Console.WriteLine(LS.Length);

        }

    }