9498 시험점수

public class Main{

	public static void main(String[] args){
		
		String grade = " ";
		
		Scanner a = new Scanner(System.in);
		
		int score = a.nextInt();
		
		if(score < 60) {
			grade = "F";
		}else if(score <70) {
			grade = "D";
		}else if(score <80) {
			grade = "C";
		}else if(score < 90) {
			grade = "B";
		}else {
			grade = "A";
		}
		System.out.println(grade);
	  }
    }