A piece of square paper with an area of 20 square centimeters, cut a largest circle inside it, what is the area of that circle?
一张正方形纸，面积是20平方厘米，在它里面剪一个最大的圆，那个圆的面积是多少？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>