You are given a string s[1 ... n] consisting of lowercase Latin letters. It is guaranteed that n = 2^k for some integer k ge 0 . The string s[1 ... n] is called c -good if at least one of the following three conditions is satisfied: For example: "aabc" is 'a '-good, "ffgheeee" is 'e '-good. In one move, you can choose one index i from 1 to n and replace s_i with any lowercase Latin letter (any character from 'a ' to 'z '). Your task is to find the minimum number of moves required to obtain an 'a '-good string from s (i.e. c -good string for c= 'a '). It is guaranteed that the answer always exists. You have to answer t independent test cases. Another example of an 'a '-good string is as follows. Consider the string s = "cdbbaaaa". It is an 'a '-good string, because: The first line of the input contains one integer t ( 1 <= t <= 2 cdot 10^4 ) -- the number of test cases. Then t test cases follow. The first line of the test case contains one integer n ( 1 <= n <= 131~072 ) -- the length of s . It is guaranteed that n = 2^k for some integer k ge 0 . The second line of the test case contains the string s consisting of n lowercase Latin letters. It is guaranteed that the sum of n does not exceed 2 cdot 10^5 ( sum n <= 2 cdot 10^5 ). For each test case, print the answer -- the minimum number of moves required to obtain an 'a '-good string from s (i.e. c -good string with c = 'a '). It is guaranteed that the answer exists.