 Complete the following phrase:  In 1986, the tournament briefly expanded to 24 teams. Four groups of six teams each competed in the preliminary round group stage. The top three teams in each group then competed in the second group stage, followed by a four-team knockout tournament between the top two finishers in each group. The championship contracted back down to 16 teams for the 1990 tournament. The three tournaments between 1990 and 1998, each had two group stages followed by a four-team knockout tournament to determine the medalists. The 