using System;

public class Program

{

    public static void Main()

    { /*double S;

        Console.WriteLine("Enter Score");

            S=Convert.ToDouble(Console.ReadLine());

        String Grade = (S<50)?"F":(S<60)?"D":(S<70)?"C":(S<80)?"B":"A";

            Console.WriteLine("Grade = {0}",Grade);*/

     double W;

        Console.WriteLine("Enter Score");

            W=Convert.ToDouble(Console.ReadLine());

     if (W < 50 )

         Console.WriteLine("Grade = F");

     else if (W < 60 )

         Console.WriteLine("Grade = D");

     else if (W < 70 )

         Console.WriteLine("Grade = C");

     else if (W < 80 )

         Console.WriteLine("Grade = B");

     else

         Console.WriteLine("Grade = A");

        }

}