A semicircle has a radius of 4 decimeters, what is its circumference in decimeters.
一个半圆，半径是4分米，它的周长是多少分米．
<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 4 * 1</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>