In Class 1, Class 2 and Class 3 of the sixth grade, each class sends three students to participate in a Go competition, and each student only plays a game of Go with all the students in the other two classes. The winner of each chess game gets 3 points, the loser gets 0 points, and each player gets 1 point for a draw. Competition result: Class 1 scored 25 points, Class 2 scored 23 points, and Class 3 scored 28 points. How many draw games did they play in total?
六年级一班、二班和三班，每班各派三名同学参加围棋比赛，每名同学只与另外两班的所有同学各赛一盘棋．每盘棋的胜者得3分，负者得0分，若是和棋则各得1分．比赛结果：一班得了25分，二班得了23分，三班得了28分，那么他们一共下了多少盘和棋？
<result>0</result>