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Given a string s consisting of lowercase Latin Letters, find the first non repeating character in s.
The first line contains T denoting the number of testcases. Then follows description of testcases.
Each case begins with a single integer N denoting the length of string. The next line contains the string s.
For each testcase, print the first non repeating character present in string.
Print -1 if there is no non repeating character.