Codeforces Round 267 (Div. 2) |
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Finished |
After you have read all the problems, probably, you think Alex is genius person. That's true! One day he came up with the following task.
Given a sequence of integer numbers a_{1}, a_{2}, ..., a_{n}. You are to find a longest sequence b_{1}, b_{2}, ..., b_{4m}, that satisfies the following conditions:
And finally... Alex had given this complicated task to George, and George gave it to you. Help George to cope with the task.
The first line contains a single integer n (1 ≤ n ≤ 5·10^{5}). The next line contains n integers a_{1}, a_{2}, ..., a_{n} (1 ≤ a_{i} ≤ 10^{9}).
In the first line print a single integer 4m — the maximal possible length of required sequence b. In the second line print 4m integers b_{1}, b_{2}, ..., b_{4m}, that is required sequence.
If there are multiple optimal answers you may print any of them.
4
3 5 3 5
4
3 5 3 5
10
35 1 2 1 2 35 100 200 100 200
8
1 2 1 2 100 200 100 200
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