The diameter of a circular island is 50m, the middle is a circular flower bed with a diameter of 20m, and the other places are lawns. What is the size of the lawn?
一个圆形环岛的直径是50m，中间是一个直径为20m的圆形花坛，其他地方是草坪．草坪的占地面积是多少？
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

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

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">625 - 100</gadget>
<output>525</output>

<gadget id="calculator">3.14 * 525</gadget>
<output>1_648.5</output>

<result>1_648.5</result>