Cut the largest circle out of a square, given the side length of the square is 20m, what is the area of the circle.
在正方形中剪一个最大的圆，已知正方形边长为20m，圆面积为多少．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>