Mr.Faisal, now, you overstay for 18 days, not a long time, if you surrender yourself to police and apologize for your fault in a good attitude, maybe the kind-hearted police won't ask you to pay for the penalty, he will give you a short-term visa, generally for a few days, to exit China. You won't be prohibitted to reentry for 5 years, please don't worry, please bear in mind that take a good attitue to this issue, please don't irritate the police.