A lotus leaf grows double every day, and the pond is covered on the 12th day. Find the day when half of the pond is covered.
一种荷叶每天长大1倍，第12天把池塘盖满，求盖满池塘的一半时是第多少天．
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<result>11</result>