import java.util.*;

public class Grader {
	public static void main(String [] args) {
		Scanner scanner = new Scanner(System.in);

		System.out.print("Midterm: ");
		int midterm = scanner.nextInt();
		System.out.print("Final: ");
		int finalExam = scanner.nextInt();

		double average = (midterm + finalExam) / 2.0;

		String grade;
		if (average >= 90)
			grade = "A";
		else if (average >= 80)
			grade = "B";
		else if (average >= 70)
			grade = "C";
		else if (average >= 60)
			grade = "D";
		else
			grade = "F";

		System.out.println("average: " + average + " grade: " + grade);
	}
}