B"Given is a string s of length n . In one operation you can select the lexicographically largest ^ dagger subsequence of string s and cyclic shift it to the right ^ ddagger . Your task is to calculate the minimum number of operations it would take for s to become sorted, or report that it never reaches a sorted state. ^ dagger A string a is lexicographically smaller than a string b if and only if one of the following holds: ^ ddagger By cyclic shifting the string t_1t_2 ldots t_m to the right, we get the string t_mt_1 ldots t_{m-1} . Each test consists of multiple test cases. The first line contains a single integer t ( 1 <= t <= 10^4 ) -- the number of test cases. The description of the test cases follows. The first line of each test case contains a single integer n ( 1 <= n <= 2 cdot 10^5 ) -- the length of the string s . The second line of each test case contains a single string s of length n , consisting of lowercase English letters. It is guaranteed that sum of n over all test cases does not exceed 2 cdot 10^5 . For each test case, output a single integer -- the minimum number of operations required to make s sorted, or -1 if it's impossible. In the first test case, the string s is already sorted, so we need no operations. In the second test case, doing one operation, we will select cb and cyclic shift it. The string s is now abc which is sorted. In the third test case, s cannot be sorted. In the fourth test case we will perform the following operations: Thus, we need 2 operations. "...