using System;

public class Program

{

    public static void Main()

    {

        int scr;

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

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

            Console.WriteLine("A");

        else if(scr>=85 && scr<90)

            Console.WriteLine("B+");

        else if(scr>=80 && scr<85)

            Console.WriteLine("B");

        else if(scr>=75 && scr<80)

            Console.WriteLine("C+");

        else if(scr>=70 && scr<75)

            Console.WriteLine("C");

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

            Console.WriteLine("D+");

        else if(scr>=60 && scr<65)

            Console.WriteLine("D");

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

            Console.WriteLine("F");

        else if(scr<0)

            Console.WriteLine("Error : Value must be greater than or equal to 0.");

        else

            Console.WriteLine("Error : Value must be less than or equal to 100.");

    }

}