The school martial arts team designed a contact method for the convenience of communication. Once something happens, the coach will notify the two captains at the same time, and then the two captains will notify the two students at the same time, and so on, each of them will notify two people at the same time. If it takes 1 minute to notify two people at the same time, how many students can be notified in 4 minutes.
学校武术队为了联络方便，设计一种联络方式．一旦有事，先由教练同时通知两位队长，这两位队长再分别同时通知两名同学，依此类推，每人再同时通知两个人．如果每同时通知两人共需1分钟，4分钟可以通知到多少名同学．
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">2 * 2 * 2</gadget>
<output>8</output>

<gadget id="calculator">2 * 2 * 2 * 2</gadget>
<output>16</output>

<gadget id="calculator">2 + 4 + 8 + 16</gadget>
<output>30</output>

<result>30</result>