Choosing Teams

总共有n个人，每个人最多参加5场比赛，现在给出每个人已经参加过的比赛次数，要组尽可能多的队伍去继续参加比赛，每支队伍3个人，要求组成的队伍至少再参加k场比赛，问最多可以组几个队 感谢@csath99 提供的翻译

The Saratov State University Olympiad Programmers Training Center (SSU OPTC) has $ n $ students. For each student you know the number of times he/she has participated in the ACM ICPC world programming championship. According to the ACM ICPC rules, each person can participate in the world championship at most 5 times. The head of the SSU OPTC is recently gathering teams to participate in the world championship. Each team must consist of exactly three people, at that, any person cannot be a member of two or more teams. What maximum number of teams can the head make if he wants each team to participate in the world championship with the same members at least $ k $ times?

The first line contains two integers, $ n $ and $ k $ $ (1<=n<=2000; 1<=k<=5) $ . The next line contains $ n $ integers: $ y_{1},y_{2},...,y_{n} $ $ (0<=y_{i}<=5) $ , where $ y_{i} $ shows the number of times the $ i $ -th person participated in the ACM ICPC world championship.

Print a single number — the answer to the problem.

5 2
0 4 5 1 0

1

6 4
0 1 2 3 4 5

0

6 5
0 0 0 0 0 0

2

In the first sample only one team could be made: the first, the fourth and the fifth participants. In the second sample no teams could be created. In the third sample two teams could be created. Any partition into two teams fits.