There is a cylindrical water pipe with an inner diameter of 20 cm, and the flow rate of water in the pipe is 40 cm per second, how many cubic centimeters of water flow through it per second.
有一个圆柱形水管，内直径为20厘米，水在管内的流速为每秒40厘米，每秒流过的水是多少立方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100 * 40</gadget>
<output>12_560</output>

<result>12_560</result>