题面

Constraints

Time Limit: 1 secs, Memory Limit: 32 MB

Description

Dr lee cuts a string S into 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