vize1 = int(input("Vize1:"))
vize2 = int(input("Vize2:"))
final = int(input("Final:"))


genel_not = vize1 * 3/10 + vize2 * 3/10 + final * 4/10
if (genel_not >= 90):
print("AA")
elif (genel_not >= 85):
print("BA")
elif (genel_not >= 80):
print("BB")
elif (genel_not >= 75):
print("CB")
elif (genel_not >= 70):
print("CC")
elif (genel_not >= 65):
print("DC")
elif (genel_not >= 60):
print("DD")
elif (genel_not >= 55):
print("FD")
else:
print("FF")