A caterpillar grows from a larva to an adult, doubling in size every day, and can grow to 16 cm in 16 days. How many days it can grow to 4 cm.
一条毛毛虫由幼虫长到成虫，每天长一倍，16天能长到16厘米．它多少天可以长到4厘米．
<gadget id="calculator">16 - 2</gadget>
<output>14</output>

<result>14</result>