B'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 <= q x <= q 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} . The first line contains a single integer t ( 1 <= q t <= q 1000 ) -- the number of test cases. The first line of each test case contains a single integer n ( 1 <= q n <= q 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. For each test case, output a single integer -- the minimum alphabet size required to so that Atilla can write his message s . 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} ). '...