378QAQ has a string $$$s$$$ of length $$$n$$$. Define the core of a string as the substring$$$^\dagger$$$ with maximum lexicographic$$$^\ddagger$$$ order.

For example, the core of "$$$\mathtt{bazoka}$$$" is "$$$\mathtt{zoka}$$$", and the core of "$$$\mathtt{aaa}$$$" is "$$$\mathtt{aaa}$$$".

378QAQ wants to rearrange the string $$$s$$$ so that the core is lexicographically minimum. Find the lexicographically minimum possible core over all rearrangements of $$$s$$$.

$$$^\dagger$$$ A substring of string $$$s$$$ is a continuous segment of letters from $$$s$$$. For example, "$$$\mathtt{defor}$$$", "$$$\mathtt{code}$$$" and "$$$\mathtt{o}$$$" are all substrings of "$$$\mathtt{codeforces}$$$" while "$$$\mathtt{codes}$$$" and "$$$\mathtt{aaa}$$$" are not.

$$$^\ddagger$$$ A string $$$p$$$ is lexicographically smaller than a string $$$q$$$ if and only if one of the following holds:

$$$p$$$ is a prefix of $$$q$$$, but $$$p \ne q$$$; or
in the first position where $$$p$$$ and $$$q$$$ differ, the string $$$p$$$ has a smaller element than the corresponding element in $$$q$$$ (when compared by their ASCII code).

For example, "$$$\mathtt{code}$$$" and "$$$\mathtt{coda}$$$" are both lexicographically smaller than "$$$\mathtt{codeforces}$$$" while "$$$\mathtt{codeforceston}$$$" and "$$$\mathtt{z}$$$" are not.

Input

Each test contains multiple test cases. The first line contains the number of test cases $$$t$$$ ($$$1\leq t\leq 10^5$$$). The description of the test cases follows.

The first line of each test case contains a single integer $$$n$$$ ($$$1\leq n\leq 10^6$$$) — the length of string $$$s$$$.

The next line of each test case contains the string $$$s$$$ of length $$$n$$$. The string $$$s$$$ consists of lowercase English letters.

It is guaranteed that the sum of $$$n$$$ over all test cases does not exceed $$$10^6$$$.

Output

For each test case, output the lexicographically minimum possible core over all rearrangements of $$$s$$$.

Note

In the first test case, all possible rearrangements and their corresponding cores are as follows:

"$$$\mathtt{qaq}$$$", its core is "$$$\mathtt{qaq}$$$".
"$$$\mathtt{aqq}$$$", its core is "$$$\mathtt{qq}$$$".
"$$$\mathtt{qqa}$$$", its core is "$$$\mathtt{qqa}$$$".

So the core with the minimum lexicographic order in all rearrangement plans is "$$$\mathtt{qaq}$$$".

378QAQ and Core

Examples