score = float(input("Enter the score : "))

if 0 < score < 10:
	if score < 0.6:
		print('F')
	elif score < 0.7:
		print('D')
	elif score < 0.8:
		print('C')
	elif score < 0.9:
		print('B')
	else:
		print('A')
else:
	print("error")
