What is the circumference of a semicircle with a radius of 4 cm?
半径是4厘米的半圆，周长是多少厘米．
<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

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

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

<result>20.56</result>