A caterpillar grows from a larva to an adult, doubles in size every day, and can grow to 20 cm in 30 days. How much does it take to grow to 5 cm?
一条毛毛虫由幼虫长成成虫，每天长大一倍，30天能长到20厘米，长到5厘米时要用多少．
<gadget id="calculator">30 - 1 - 1</gadget>
<output>28</output>

<result>28</result>