The radius of a semicircular fish pond is 4 meters, what is its circumference in meters?
一个半圆形鱼池的半径是4米，它的周长是多少米？
<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">12.56 + 8</gadget>
<output>20.56</output>

<result>20.56</result>