print('请输入你的分数:',end = '')
temp = input()
while not temp.isdigit() or int(temp) >100 or int(temp) < 0:
print('格式错误,请输入0-100的整数:')
temp = input()
num = int(temp)
if 90 <= num <=100:
print('A')
elif 80 <= num < 90:
print('B')
else:
if 60 <= num <=80:
print('C')
else:
print('D')