Bob has been provided a string \(S\) of size \(N\) containing lowercase characters. He took two empty strings, \(U\) and \(V\), and performed the following operations:

1. Extract the first character from string \(S\) and append it at the end of string \(U\).
2. Extract the last character from string \(U\) and append it at the end of string \(V\).

Bob can perform the above operations any number of times. After some operations, he wants to get the string \(S\) and \(U\) empty, and string \(V\) should be lexicographically minimum. 

Your task is to help Bob find the lexicographically minimum possible string \(V\) that can be formed.

Input Format:

• The first line of input contains an integer \(T\), denoting the number of test cases.
• For each test case, the first line will contain integer \(N\), the size of the input string \(S\), and the second line will contain the string \(S\) itself.

Output format:

For each test case, print the lexicographically minimum possible string \(V\) that can be formed.

Constraints:

\(1 <= T <= 5\)

\(1 <= N <= 10^5\)

\(S[i]\) will be a lowercase english character.