What is the circumference of a semicircle with a radius of 10 cm?
半径是10厘米的半圆，它的周长是多少厘米．
<gadget id="calculator">3.14 * 10</gadget>
<output>31.4</output>

<gadget id="calculator">2 * 10</gadget>
<output>20</output>

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

<result>51.4</result>