# -*- coding: utf-8 -*-
"""
Created on Sat Mar 21 11:56:57 2020

@author: User
"""


score=input("請輸入你的成績")

score=int(score)

if score>=90:
    print('A')
    
elif score>=75:
    print('B')

elif score>=60:
    print('c')
    
else:
    print('D')           