There is an urgent notice during the summer vacation. Teacher Li from the school office needs to notify the school teachers to attend a meeting at the school. If you use the phone call, one person will be notified every minute, and each teacher will notify others immediately after receiving the notification. So, how many people can be notified in 3 minutes at most.
暑假有一个紧急通知，学校办公室李老师需要通知学校老师到学校开会．如果用打电话的方式，每分钟通知1人，每个老师接到通知后马上通知别人．那么，3分钟最多可以通知多少人．
<gadget id="calculator">1 + 2 + 4</gadget>
<output>7</output>

<result>7</result>