using System;

​

public class Program

{

    public static void Main()

    {

        int mrk;

        mrk = Convert.ToInt32(Console.ReadLine());

        if ((mrk >= 90) && (mrk <= 100))

            Console.WriteLine("Grade A");

        else if ((mrk >= 80) && (mrk < 90))

            Console.WriteLine("Grade B");

        else if ((mrk >= 70) && (mrk < 80))

            Console.WriteLine("Grade C");

        else if ((mrk >= 60) && (mrk < 70))

            Console.WriteLine("Grade D");

        else if ((mrk >= 0) && (mrk < 60))

            Console.WriteLine("Grade F");

        else

            Console.WriteLine("Invalid input marks");

    }

}