The water surface area occupied by duckweed in the pond doubles every day, and after 62 days the whole pond is covered with duckweed. How many days did it take for the duckweed to grow to half the surface of the pond?
浮萍在池塘里所占水面面积每天增加一倍，经过62天整个池塘长满了浮萍．浮萍长到半个池塘水面时，用了多少天时间．
<gadget id="calculator">62 - 1</gadget>
<output>61</output>

<result>61</result>