square iron sheet with a circumference of 80dm should cut out the largest circle, what is the area of this circle?
一个周长为80dm的正方形铁皮，要剪下一个最大的圆，这个圆的面积是多少．
<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<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>