A caterpillar grows from a larva to an adult, doubling in size every day, and can grow to 16 cm in 16 days. Ask how many days it can grow to 8 cm.
一条毛毛虫由幼虫长到成虫，每天长大一倍，16天能长到16厘米．问它多少天可以长到8厘米．
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<result>15</result>