There is a circular fountain with a diameter of 50m in a park. A sidewalk with a width of 3m is built around the fountain. What is the area of the sidewalk in square meters?
某公园有一个直径为50m的圆形喷水池，在这个喷水池的周围修一条3m宽的人行道，人行道的面积是多少平方米？
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">25 + 3</gadget>
<output>28</output>

<gadget id="calculator">28 ** 2</gadget>
<output>784</output>

<gadget id="calculator">3.14 * 784</gadget>
<output>2_461.76</output>

<gadget id="calculator">25 ** 2</gadget>
<output>625</output>

<gadget id="calculator">3.14 * 625</gadget>
<output>1_962.5</output>

<gadget id="calculator">2_461.76 - 1_962.5</gadget>
<output>499.26</output>

<result>499.26</result>