The diameter of a circular cistern is 400 meters, how many square meters does this cistern occupy?
一个圆形蓄水池的直径是400米，这个蓄水池占地多少平方米？
<gadget id="calculator">400 / 2</gadget>
<output>200</output>

<gadget id="calculator">200 ** 2</gadget>
<output>40_000</output>

<gadget id="calculator">3.14 * 40_000</gadget>
<output>125_600</output>

<result>125_600</result>