For a road 800 meters long, a willow tree should be planted every 20 meters on both sides of the road from the beginning to the end. How many willow seedlings should be planted in total?
一条长800米的公路，要在公路的两侧从头到尾每隔20米栽一棵柳树，共栽多少棵柳树苗．
<gadget id="calculator">800 / 20</gadget>
<output>40</output>

<gadget id="calculator">40 + 1</gadget>
<output>41</output>

<gadget id="calculator">41 * 2</gadget>
<output>82</output>

<result>82</result>