Given a semicircle with a radius of 5 cm, what is its perimeter?
现有一个半径为5cm的半圆形，他的周长是多少．
<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 5 * 1</gadget>
<output>15.7</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">15.7 + 10</gadget>
<output>25.7</output>

<result>25.7</result>