Start to plant trees on one side of the road, plant one tree at 5 meters, how many trees should be planted at 100 meters. (both ends planted)
在马路的一边开始植树，5米植一棵，100米要植多少棵树．(两头都植)
<gadget id="calculator">100 / 5</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>