Mr. Lin has an urgent matter to notify 30 students. If he uses the telephone, he will notify one person every minute. After each person receives the notification, he will immediately notify the other person. It will take at least a few minutes to notify everyone.
林老师有急事要通知30名同学，如果用打电话的方式，每分钟通知1人，每个人接到通知后马上通知另一个人，最少用多少分钟就能通知每个人．
<result>5</result>