Description:
In order to write a string, Atilla needs to first learn all letters that are contained in the string.
Atilla needs to write a message which can be represented as a string $$$s$$$. He asks you what is the minimum alphabet size required so that one can write this message.
The alphabet of size $$$x$$$ ($$$1 \leq x \leq 26$$$) contains only the first $$$x$$$ Latin letters. For example an alphabet of size $$$4$$$ contains only the characters $$$\texttt{a}$$$, $$$\texttt{b}$$$, $$$\texttt{c}$$$ and $$$\texttt{d}$$$.
Input Format:
The first line contains a single integer $$$t$$$ ($$$1 \leq t \leq 1000$$$) — the number of test cases.
The first line of each test case contains a single integer $$$n$$$ ($$$1 \leq n \leq 100$$$) — the length of the string.
The second line of each test case contains a string $$$s$$$ of length $$$n$$$, consisting of lowercase Latin letters.
Output Format:
For each test case, output a single integer — the minimum alphabet size required to so that Atilla can write his message $$$s$$$.
Note:
For the first test case, Atilla needs to know only the character $$$\texttt{a}$$$, so the alphabet of size $$$1$$$ which only contains $$$\texttt{a}$$$ is enough.
For the second test case, Atilla needs to know the characters $$$\texttt{d}$$$, $$$\texttt{o}$$$, $$$\texttt{w}$$$, $$$\texttt{n}$$$. The smallest alphabet size that contains all of them is $$$23$$$ (such alphabet can be represented as the string $$$\texttt{abcdefghijklmnopqrstuvw}$$$).