Alex and Complicated Task
Description
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 a1, a2, ..., an. You are to find a longest sequence b1, b2, ..., b4m, that satisfies the following conditions:
- b4k + 1 = b4k + 3 for all valid integer k;
- b4k + 2 = b4k + 4 for all valid integer k;
- sequence b is subsequence of a (not necessarily contiguous subsequence).
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 ≤ 5·105). The next line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 109).
In the first line print a single integer 4m — the maximal possible length of required sequence b. In the second line print 4m integers b1, b2, ..., b4m, that is required sequence.
If there are multiple optimal answers you may print any of them.
Input
The first line contains a single integer n (1 ≤ n ≤ 5·105). The next line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 109).
Output
In the first line print a single integer 4m — the maximal possible length of required sequence b. In the second line print 4m integers b1, b2, ..., b4m, that is required sequence.
If there are multiple optimal answers you may print any of them.
Samples
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