On a circular runway with a circumference of 400 meters, there are two points A and B 100 meters apart. Two people, A and B, run from the two points A and B with their backs facing each other. When they meet, B turns around and runs in the same direction as A. , when A runs to A, B happens to run to B. If A and B run at the same speed and direction in the future, when A catches up with B, how many meters has A run since the start?
周长为400米的环形跑道上，有相距100米的A、B两点，甲乙两人分别从A、B两点背向而跑，两人相遇后，乙即转身与甲同向而跑，当甲跑到A时，乙恰好跑到B．如果以后甲、乙跑的速度和方向都不变，那么甲追上乙时，从出发开始，甲共跑了多少米？
<gadget id="calculator">400 / 2</gadget>
<output>200</output>

<gadget id="calculator">200 - 100</gadget>
<output>100</output>

<gadget id="calculator">400 - 100</gadget>
<output>300</output>

<gadget id="calculator">300 * 2</gadget>
<output>600</output>

<gadget id="calculator">400 + 600</gadget>
<output>1_000</output>

<result>1_000</result>