Install street lights on both sides of a street with a total length of 180m (no installation at both ends). Install one every 6m, how many street lights should be installed in total?
在一条全长为180m的街道两旁安装路灯(两端都不安装)．每隔6m安装一盏，一共要安装多少盏路灯？
<gadget id="calculator">180 / 6</gadget>
<output>30</output>

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

<gadget id="calculator">29 * 2</gadget>
<output>58</output>

<result>58</result>