There are 25 horses, and each runs at different constant speeds. If you want to find the 5 fastest horses, what is the minimum number of races needed, if each race can have five horses at most
有25匹马，每匹马都以一个固定不变的速度奔跑，每匹马的速度都不一样，如果让你找出跑的最快的5匹马，最少需要组织多少场比赛？注：每场比赛最多只能5匹马参赛。