using System;

public class Program

{

    public static void Main()

    {

        Console.Write("Enter a letter grade: ");

        string letter = Console.ReadLine();

        Char parsedValue;

        bool success = Char.TryParse(letter,out parsedValue);

        if(success){

            Char l = Convert.ToChar(letter);

            if(char.IsLetter(l))

            l = Char.ToUpper(l);

        switch(l)

        {

            case 'A':

            Console.Write("Excellent!");

            break;

            case 'B':

            Console.Write("Good");

            break;

            case 'C':

            Console.Write("Okay");

            break;

            case 'D':

            Console.Write("Try better!!");

            break;

            case 'F':

            Console.Write("Not so good:(");

            break;

            default:

            Console.Write("Invalid Input");

            break;

        }

       }else

            Console.Write("Invalid Input");

    }

}