Cut out the largest circle on a piece of rectangular paper with a length of 5dm and a width of 4dm. What is the area of this circle in d㎡?
在一张长5dm，宽4dm的长方形纸上剪下一个最大的圆，这个圆的面积是多少d㎡．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>