score

import java.util.Scanner;

public class score
{
	public static void main(String args[]){
		Scanner sc=new Scanner(System.in);
		while(sc.hasNextDouble()){

			double scoer=sc.nextDouble();
			if(scoer<60)
				System.out.println("D");
			else if(scoer<70)
				System.out.println("C");
			else if(scoer<85)
				System.out.println("B");
			else 
				System.out.println("A");
		}
		sc.close();
	}
}