Plant trees on one side of a road at intervals of 2 meters. A total of 18 trees are planted (both ends are planted). How many meters is this road?
在一条路的一侧植树，每隔2米植一棵，共植了18棵(两端都植)，这条路有多少米．
<gadget id="calculator">18 - 1</gadget>
<output>17</output>

<gadget id="calculator">17 * 2</gadget>
<output>34</output>

<result>34</result>