Students plant trees on one side of the river. The river bank is 64 meters long. Plant a tree every 4 meters. Neither end is planted. How many trees are needed in total?
同学们到河的一边种树，河岸长64米，每隔4米种一棵树，两端都不种，共需要多少棵树？
<gadget id="calculator">64 / 4</gadget>
<output>16</output>

<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<result>15</result>