Xenia and Divisors

题意翻译

一共有$n(n< 10^5)$个正整数，每个数不大于$7$。现在要求选出$\frac{n}{3}$个数对$(a,b,c)$，使得$a<b<c$，且$a$整除$b$，$b$整除$c$。保证$n$是$3$的倍数。 如果无解，输出$-1$。

题目描述

Xenia the mathematician has a sequence consisting of $ n $ ( $ n $ is divisible by 3) positive integers, each of them is at most 7. She wants to split the sequence into groups of three so that for each group of three $ a,b,c $ the following conditions held: - $ a&lt;b&lt;c $ ; - $ a $ divides $ b $ , $ b $ divides $ c $ . Naturally, Xenia wants each element of the sequence to belong to exactly one group of three. Thus, if the required partition exists, then it has  groups of three. Help Xenia, find the required partition or else say that it doesn't exist.

输入输出格式

输入格式

The first line contains integer $ n $ $ (3<=n<=99999) $ — the number of elements in the sequence. The next line contains $ n $ positive integers, each of them is at most 7. It is guaranteed that $ n $ is divisible by 3.

输出格式

If the required partition exists, print  groups of three. Print each group as values of the elements it contains. You should print values in increasing order. Separate the groups and integers in groups by whitespaces. If there are multiple solutions, you can print any of them. If there is no solution, print -1.

输入输出样例

输入样例 #1

6
1 1 1 2 2 2

输出样例 #1

-1

输入样例 #2

6
2 2 1 1 4 6

输出样例 #2

1 2 4
1 2 6