What is the area of a circle surrounded by a wire with a length of 12.56 decimeters?
用一条长12.56分米的铁丝围成一个圆，它的面积是多少．
<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>