CF1760B.Atilla's Favorite Problem

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 $\texttt{d}$.

为了书写一个字符串，阿提拉需要首先学会该字符串中包含的所有字母。

阿提拉需要书写一条可表示为字符串 $s$ 的消息。他向你询问：能够书写该消息所需的最小字母表大小是多少？

大小为 $x$（$1 \leq x \leq 26$）的字母表仅包含前 $x$ 个拉丁字母。例如，大小为 $4$ 的字母表仅包含字符 $\texttt{a}$、$\texttt{b}$、$\texttt{c}$ 和 $\texttt{d}$。

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.

第一行包含一个整数 $t$（$1 \leq t \leq 1000$）—— 测试用例的数量。

每个测试用例的第一行包含一个整数 $n$（$1 \leq n \leq 100$）—— 字符串的长度。

每个测试用例的第二行包含一个长度为 $n$ 的字符串 $s$，由小写拉丁字母组成。

For each test case, output a single integer — the minimum alphabet size required to so that Atilla can write his message $s$.

对于每个测试用例，输出一个整数——Atilla 能够写出消息 $s$ 所需的最小字母表大小。

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 $\texttt{abcdefghijklmnopqrstuvw}$).

对于第一个测试用例，Atilla 只需知道字符 $\texttt{a}$，因此仅包含 $\texttt{a}$ 的大小为 $1$ 的字母表就已足够。

对于第二个测试用例，Atilla 需要知道字符 $\texttt{d}$、$\texttt{o}$、$\texttt{w}$、$\texttt{n}$。包含所有这些字符的最小字母表大小为 $23$（这样的字母表可表示为字符串 $\texttt{abcdefghijklmnopqrstuvw}$）。