## Problem G: Catenyms

A catenym is a pair of words separated by a period such that the last letter of the first word is the same as the first letter of the second. For example, the following are catenyms:
```dog.gopher
gopher.rat
rat.tiger
aloha.aloha
arachnid.dog
```
A compound catenym is a sequence of three or more words separated by periods such that each adjacent pair of words forms a catenym. For example,
```aloha.aloha.arachnid.dog.gopher.rat.tiger
```
Given a dictionary of lower case words, you are to find a compound catenym that contains each of the words exactly once. The first line of standard input contains t, the number of test cases. Each test case begins with 3 <= n <= 1000 - the number of words in the dictionary. n distinct dictionary words follow; each word is a string of between 1 and 20 lowercase letters on a line by itself. For each test case, output a line giving the lexicographically least compound catenym that contains each dictionary word exactly once. Output "***" if there is no solution.

```2
6
aloha
arachnid
dog
gopher
rat
tiger
3
oak
maple
elm
```

### Output for Sample Input

```aloha.arachnid.dog.gopher.rat.tiger
***
```