Use a fence to surround a semicircular chicken house with a diameter of 5 meters against the wall. How long is the fence?
靠墙用篱笆围一个直径是5米的半圆形鸡舍，篱笆长多少．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">3.14 * (5/2)</gadget>
<output>7.85</output>

<result>7.85</result>