20 rabbits stand in a row, and there is a mushroom between every two rabbits. How many mushrooms are there in total?
20个兔子站成一排，每两只兔子中间有一个蘑菇，一共有多少个蘑菇．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<result>19</result>