The diameter of a circular fish pond is 40 meters. There is a gravel road with a width of 1 meter around the fish pond. What is the area of this gravel road in square meters?
一个圆形养鱼池的直径是40米，在这个鱼池的周围有一条宽1米的石子路，这条石子路的面积是多少平方米？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<gadget id="calculator">21 ** 2</gadget>
<output>441</output>

<gadget id="calculator">3.14 * 441</gadget>
<output>1_384.74</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400</gadget>
<output>1_256</output>

<gadget id="calculator">1_384.74 - 1_256</gadget>
<output>128.74</output>

<result>128.74</result>