# coding:utf-8
m=input("请输入成绩：")
m=float(m)
if m<0 or m>100:
    print("Invalid")
elif m>=90:
    print("A")
elif m>=80:
    print("B")
elif m>=70:
    print("C")
elif m>=60:
    print("D")
else:
    print("E")