Cut a pentagon into two parts along a straight line, cut one of them into two parts along a straight line, then cut one of the three parts into two parts along a straight line, ..., and so on, to get 20 pentagons , at least how many times to cut.
将一个五边形沿一条直线切成两部分，其中之一再沿一条直线切成两部分，然后再沿一条直线将三部分之一切成两部分，…，如此下去，要得到20个五边形，最少要切多少次．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<result>19</result>