The speeds of athlete A and athlete B on flat ground are 140 meters per minute and 100 meters per minute respectively. However, when they go downhill, the speed of both increases by 20 meters per minute; when they go uphill, the speed of both decreases by 20 meters per minute. Now they start from the top of the slope at the same time, run to the bottom of the slope, and then run back, and so on. The distance between the position when they met face-to-face for the third time and the position where player A catches up with player B for the third time is 200 meters. What is the length of this slope in meters?
运动员A和运动员B在平地上的速度分别为每分钟140米与每分钟100米．但是，当他们下坡时，两者的速度每分钟都增加20米；上坡时，两者的速度则每分钟都减少20米．今他们同时从斜坡顶开始出发，跑到斜坡底后，再往回跑，如此继续下去．当他们第三次面对面相遇时的位置，与运动员A第三次追上运动员B的位置，这两个位置之间的距离是200米．试问这个斜坡的长度是多少米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">200 / (1/2)</gadget>
<output>400</output>

<result>400</result>