# -*- coding: utf-8 -*-
"""
Created on Mon Feb  1 14:36:23 2021

@author: MTAEXAM
"""

score=int(input("分數:"))
if score<100 and score>0:
    if   score>=90:
        print("A")
    elif score>=80:
        print("B")
    elif score>=70:
        print("C")
    elif score>=60:
        print("D")
    else:
        print("Not Good")
    
else:
    print("error")
    

    