using System;

public class Program

{

    public static void Main()

    {

        string readResult;

        bool validEntry = false;

        Console.WriteLine("Enter a string contatining a least three charactres: ");

        do

        {

            readResult = Console.ReadLine();

            if(readResult != null)

            {

                if (readResult.Length >= 3)

                {

                    validEntry = true; 

                }

                else

                {

                    Console.WriteLine("You input is invalid, please try again.");

                }

            }

        } while (validEntry == false);

    }

}