There are 15 stations (including the starting station and the terminal station) on a certain bus line. During the driving process of the bus from the starting station to the terminal station, the people who get on the bus at each station (including the starting station) happen to be in the following stations. Each has 1 person to get off the bus. To make the passenger have seats when the car is running, how many passenger seats must be arranged in the car at least?
某公共汽车线路上共有15个车站(包括起点站和终点站)，公共汽车从起点站到终点站的行驶过程中，每一站(包括起点站)上车的人中恰好在以后的各站都各有1人下车，要使汽车在行驶中乘客都有座位，那么在车上至少要安排乘客座位多少个？
<gadget id="calculator">7 * 8</gadget>
<output>56</output>

<result>56</result>