s= input("Enter score:")
x=float(s)
if x>1 or x<0:
    print("Bad Score")
elif x>= .9:
    print("A")
elif x>=.8:
    print("B")
elif x>=.7:
    print("C")
elif x>=.6:
    print("D")
elif x<.6:
    print("F")
else:
    print("Bad Score")
