using System;

public class Program

{

    public static void Main()

    {

        int marksSum = int.Parse(Console.ReadLine());

        marksSum += int.Parse(Console.ReadLine());

        marksSum += int.Parse(Console.ReadLine());

        marksSum += int.Parse(Console.ReadLine());

        marksSum += int.Parse(Console.ReadLine());

        double avg = Math.Round(marksSum / (double)5, 2);

        if (5.50 <= avg && avg <= 6)

        {

            Console.WriteLine("A " + avg);

        }

        else if (4.50 <= avg && avg <= 5.49)

        {

            Console.WriteLine("B " + avg);

        }

        else if (3.50 <= avg && avg <= 4.49)

        {

            Console.WriteLine("C " + avg);

        }

        else if (3.00 <= avg && avg <= 3.49)

        {

            Console.WriteLine("D " + avg);

        }

        else if (2.00 <= avg && avg <= 2.99)

        {

            Console.WriteLine("F " + avg);

        }

    }

}