Cut the largest circle out of a piece of rectangular paper with a length of 5 cm and a width of 4 cm. What is the area of this circle in the area of the paper?
用一张长5厘米，宽4厘米的长方形纸剪一个最大的圆，这个圆的面积占这张纸面积的多少．
<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>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">12.56 / 20</gadget>
<output>0.628</output>

<result>0.628</result>