The diameter of a circular island is 40 meters, the middle is a circular flower bed with a diameter of 10 meters, and the rest is lawn. What is the size of the lawn?
一个圆形环岛的直径是40米，中间是一个直径为10米的圆形花坛，其它的地方是草坪．草坪的占地面积是多少？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

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

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

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

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<gadget id="calculator">1_256 - 78.5</gadget>
<output>1_177.5</output>

<result>1_177.5</result>