def check_class(ip_addr):
    if ip_addr.startswith("10."):
        print("This a Class A address")
    elif ip_addr.startswith("172."):
        print("This is a Class B address")
    elif ip_addr.startswith("192."):
        print("This is a Class C address")
    else:
        print("I'm not sure what the Class is")


check_class("10.0.0.5")
check_class("172.16.1.1")
check_class("2001:db8::1")