using System;

public class Program

{

    public static void Main()

    {

        string telephonenumber;

        do

        {

            Console.WriteLine("Please enter your number: ");

            telephonenumber = Console.ReadLine();

            if(telephonenumber.Length != 11)

            {

                Console.WriteLine("incorrect length please re-enter");

            }

        }

        while (telephonenumber.Length != 11);

        Console.WriteLine("Welcome to the system");

    }

}