large river has two ports, A and B. The water flows from A to B at a speed of 4 kilometers per hour. Ships A and B set off from A and B respectively, and sail back and forth between A and B without stopping. The speed of ship A in still water is 20 kilometers per hour, and the speed of ship B in still water is 28 kilometers per hour. How many times did the two ships meet before they first met at the port?
一条大河有A、B两个港口，水由A流向B，水流速度是每小时4千米，甲、乙两船分别从A、B出发，各自不停地在A、B之间往返航行，甲船在静水中的速度是每小时20千米，乙船在静水中的速度是每小时28千米，两船在第一次在港口相遇前发生过多少次相遇．
<result>3</result>