https://www.acmicpc.net/problem/9498
import java.util.*;
public class Main {
public static void main(String args[]) {
Scanner s=new Scanner(System.in);
int n=s.nextInt();
if(n>=90) System.out.print("A");
else if(n>=80) System.out.print("B");
else if(n>=70) System.out.print("C");
else if(n>=60) System.out.print("D");
else System.out.print("F");
}
}