What is the area of a circle surrounded by 31.4 cm iron wire (not counting the joints).
用31.4厘米的铁丝围成一个圆形(接口处不计)，这个圆形的面积是多少．
<gadget id="calculator">31.4 / 3.14 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>