Two people, A and B, are swimming in the same swimming lane with a length of 50 meters. A swims back and forth every 3 minutes and 20 seconds, and B swims a back and forth every 2 minutes and 40 seconds. A swims 40 meters first, and B starts from the same starting point. When A swims 1000 meters, how many times is he caught up by B from behind?
甲、乙二人在长50米的同一条泳道里游泳，甲每3分20秒游一个来回，乙每2分40秒游一个来回．甲先游40米，乙从同一起点出发，当甲游完1000米时，他被乙从后面追上几次？
<gadget id="calculator">1_000 - 200</gadget>
<output>800</output>

<gadget id="calculator">800 / 400</gadget>
<output>2</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>