The circumference of a circle is 400 meters, and a red flag is inserted every 20 meters on the circle, how many red flags are needed in total.
一个圆圈的周长是400米，在这个圆圈上每隔20米插一面红旗，一共需要多少面红旗．
<gadget id="calculator">400 / 20</gadget>
<output>20</output>

<result>20</result>