A red flag is planted every 4 meters on a circular runway. There are 100 red flags in total. How many meters is there in one week of this runway?
在一个环形跑道上每隔4米插上一面红旗，共插了100面，这个跑道的一周有多少米？
<gadget id="calculator">4 * 100</gadget>
<output>400</output>

<result>400</result>