It takes 12 days for an insect to grow from a larva to an adult, and it doubles in size every day. The adult body is 40 mm long, so how many days does it take to grow to half the adult body length?
一种昆虫从幼虫长到成虫要12天，每天长大一倍，成虫身长40毫米，那么长到成虫身体长度的一半要多少天．
<result>11</result>