road is 600 meters long, and there are trash cans placed every 20 meters on one side of the road.
一条公路长600米，路一侧每隔20米放一个垃圾桶，起点和终点是站牌，不用放，一共需要放多少个垃圾桶？
<gadget id="calculator">600 / 20</gadget>
<output>30</output>

<gadget id="calculator">30 - 1</gadget>
<output>29</output>

<result>29</result>