## Description:

Dr lee cuts a string S into N pieces , s[1],……,s[N].

Now , Dr lee gives you these N sub-string:s[1]…,s[N].T 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

## Note:

本题由旧版NOJ导入，来源：第九届中山大学程序设计竞赛预选题