Cut a largest circle from a rectangular cardboard with a length of 8 cm and a width of 4 cm. What is the area of the circle in square decimeters?
在一个长8厘米、宽4厘米的长方形纸板上剪一个最大的圆，圆的面积是多少平方分米．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<gadget id="calculator">12.56 / 100</gadget>
<output>0.1256</output>

<result>0.1256</result>