It means that the person who played 24 innings is right. The number of games for n players is n(n+ 1)/2, 36 when n=9, 28 when n=8, and 2 1 when n=7. If a person quits midway, he will participate in at least one game (otherwise it is not called midway) and at most n-2 games (if n- 1 game is full, he will not quit). So n=9 is impossible, only n=8. Someone attended four retreats.