Plant trees between two buildings with a distance of 60 meters (never plant at both ends), plant one tree every 3 meters, how many trees were planted in total.
在相距60米的两座楼房之间栽树(两端都不栽)，每隔3米栽一棵，共栽了多少棵．
<gadget id="calculator">60 / 3</gadget>
<output>20</output>

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

<result>19</result>