A hound is tied to a stake by the owner with a 5-meter-long rope, and 0.5 meters is used for the knot. What is the maximum defense range of this hound?
一只猎犬被主人用一根5米长的绳子拴在木桩上，打结处用去0.5米，这只猎犬防卫范围最大是多少平方米？
<gadget id="calculator">5 - 0.5</gadget>
<output>4.5</output>

<gadget id="calculator">4.5 ** 2</gadget>
<output>20.25</output>

<gadget id="calculator">3.14 * 20.25</gadget>
<output>63.585</output>

<result>63.585</result>