# ============================
# Coursera practicing script
# Python for Informatic Book
# CHAPTER 3
# ============================
# EX3.3


score_inp = raw_input("Score 0.0 to 1.0: ")

try:
    score = float(score_inp)

    if 0.9 <= score <= 1:
        print "A"
    elif 0.8 <= score < 0.9:
        print "B"
    elif 0.7 <= score < 0.8:
        print "C"
    elif 0.6 <= score < 0.7:
        print "D"
    elif 0.6 < score < 0.6:
        print "F"
    else:
        print "Bad score"
except:
    print "Typed numbers on the range"