A peach tree is planted between every two willow trees, and if 100 willow trees are planted, how many peach trees should be planted?
每两棵柳树中间栽一棵桃树，栽100棵柳树，应栽多少棵桃树．
<gadget id="calculator">100 - 1</gadget>
<output>99</output>

<result>99</result>