What is the area of a circular piece of iron with a circumference of 12.56m?
一块周长为12.56m的圆形铁片，它的面积是多少平方米．
<gadget id="calculator">12.56 / 3.14 / 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>