A lotus leaf doubles in size every day, and the pond is covered on the 12th day. When the pond is half covered, how many days is it?
一种荷叶每天长大一倍，第12天把池塘盖满，求盖满池塘一半时是第几天？
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<result>11</result>