What is the perimeter of a semicircle with a radius of 2?
一个半圆形，半径是2，它的周长是多少．
<gadget id="calculator">3.14 * 2</gadget>
<output>6.28</output>

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

<gadget id="calculator">6.28 + 4</gadget>
<output>10.28</output>

<result>10.28</result>