OnlineJudge 3 现已推出。点此体验新版：Substring | SDUT OnlineJudge

### Substring

Time Limit: 1000 ms
Memory Limit: 65536 KiB

#### Problem Description

Dr lee cuts a string S int N pieces, s[1],...,s[N]. Now, Dr lee gives you these N sub-strings: s[1],...,s[N]. there might be several possibilities that the string S could be. For example, if Dr. lee gives you three sub-strings {"a","ab","ac"}, the string S could be "aabac","aacab","abaac",... YOur task is to output the lexicographically smallest S.

#### Input

The first line of the input is a positive integer T. T is the number of the test cases followed. The first line of each test case is a positive integer N(1<=N<=8) which represents the number of sub-strings. After that, N lines followed. The i-th line is the i-th sub-string s[i]. Assume that the length of each sub-string is positive and less than 100.

#### Output

The output of each test is the lexicographically smallest S. No redundant spaces are needed.

#### Sample Input

1 3 a ab ac

#### Sample Output

aabac

#### Hint

#### Source

第9届中山大学程序设计竞赛预选赛