Are you pissed off with your regular expression homework? well then. here is the answer.

^([0-9]|[1-9][0-9]|1([0-9][0-9])|2([0-4][0-9]|5[0-5])).([0-9]|[1-9][0-9]|1([0-9][0-9])|2([0-4][0-9]|5[0-5])).([0-9]|[1-9][0-9]|1([0-9][0-9])|2([0-4][0-9]|5[0-5])).([0-9]|[1-9][0-9]|1([0-9][0-9])|2([0-4][0-9]|5[0-5]))$