What is the perimeter of a semicircle with a radius of 5 decimeters?
半径为5分米的半圆的周长是多少分米．
<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

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

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

<result>25.7</result>