The diameter of a circular island is 50m, in the middle is a circular flower bed with a diameter of 30m, 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30m的圆形花坛，其它地方是草坪．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">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 ** 2</gadget>
<output>225</output>

<gadget id="calculator">625 - 225</gadget>
<output>400</output>

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

<result>1_256</result>