The experimental primary school planted trees on both sides of the main road (neither ends can be planted), one tree every 6m, and a total of 120m from the starting point to the end point. How many trees are needed in total?
实验小学在主干道的两侧植树(两端都不能植)，每隔6m植一棵，从起点到终点共120m，共需要多少棵树？
<gadget id="calculator">120 / 6</gadget>
<output>20</output>

<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">19 * 2</gadget>
<output>38</output>

<result>38</result>