using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(ReturnLetterAye("24"));

    }

    public static string ReturnLetterAye(string incomingString)

    {

        if (!string.IsNullOrEmpty(incomingString)){

            int n;

            bool isNumeric = int.TryParse(incomingString, out n);

            if (isNumeric){

                return "Oh no it's a number. You can't have this";

            }else{

                if (incomingString == "I"){

                    return "i";

                }else{

                    return "An error occurred. Please try again";

                }

            }

        }else{

            return "Oh no no value";

        }

    }

}