The radius of the semicircle is 10 decimeters, what is the circumference of the semicircle?
半圆的半径是10分米，半圆的周长是多少分米．
<gadget id="calculator">2 * 10</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 10</gadget>
<output>31.4</output>

<gadget id="calculator">20 + 31.4</gadget>
<output>51.4</output>

<result>51.4</result>