using System;

​

public class Program

{

    public static void Main()

    {

        start:

            Console.WriteLine("Please enter your grade");

        string x = Console.ReadLine();

        byte grade;

        if ( byte.TryParse(x, out grade)) {

        if (grade >= 0 && grade <= 64)

        {

            Console.WriteLine("You got a F");

        }

        else if (grade >= 65 && grade <= 70)

        {

            Console.WriteLine("You got a D");

        }

        else if (grade >= 71 && grade <= 80)

        {

            Console.WriteLine("You got a C");

        }

        else if (grade >= 81 && grade <= 90)

        {

            Console.WriteLine("You got a B");

        }

        else if (grade >= 91 && grade <= 100)

        {

            Console.WriteLine("You got a A");

        }

        else

        {

            Console.WriteLine("please enter a valid number ");

            goto start;

        }

        }

        else 

        {Console.WriteLine("Please enter a number from 0-100");

         goto start;

        }

    }

}