[백준] #9498: 시험 성적

import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int score = sc.nextInt();
		
		if(score>=90 && score<=100)
			System.out.println("A");
		else if(score>=80 && score<90)
			System.out.println("B");
		else if(score>=70 && score<80)
			System.out.println("C");
		else if(score>=60 && score<70)
			System.out.println("D");
		else
			System.out.println("F");
		
	}
}