description: A string s of length n, consisting of lowercase letters of the English alphabet, is given.
  
  You must choose some number k between 0 and n. Then, you select k characters of s and permute them however you want. In this process, the positions of the other n-k characters remain unchanged. You have to perform this operation exactly once.
  
  For example, if s="andrea", you can choose the k=4 characters "a_d_ea" and permute them into "d_e_aa" so that after the operation the string becomes "dneraa".
  
  Determine the minimum k so that it is possible to sort s alphabetically (that is, after the operation its characters appear in alphabetical order).
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 1000) — the number of test cases. Then t test cases follow.
  
  The first line of each test case contains one integer n (1 ≤ n ≤ 40) — the length of the string.
  
  The second line of each test case contains the string s. It is guaranteed that s contains only lowercase letters of the English alphabet.
  
  Output
  
  For each test case, output the minimum k that allows you to obtain a string sorted alphabetically, through the operation described above.
  
  Example
  
  Input
  
  
  4
  3
  lol
  10
  codeforces
  5
  aaaaa
  4
  dcba
  
  
  Output
  
  
  2
  6
  0
  4
  
  Note
  
  In the first test case, we can choose the k=2 characters "_ol" and rearrange them as "_lo" (so the resulting string is "llo"). It is not possible to sort the string choosing strictly less than 2 characters.
  
  In the second test case, one possible way to sort s is to consider the k=6 characters "_o__force_" and rearrange them as "_c__efoor_" (so the resulting string is "ccdeefoors"). One can show that it is not possible to sort the string choosing strictly less than 6 characters.
  
  In the third test case, string s is already sorted (so we can choose k=0 characters).
  
  In the fourth test case, we can choose all k=4 characters "dcba" and reverse the whole string (so the resulting string is "abcd").
solution: import java.io.*;
  import java.util.*;
  
  public class Code {
      public static void main(String[] args) {
          try {
              FastScanner scn = new FastScanner();
              StringBuilder ans = new StringBuilder();
              int testCase = scn.nextInt();
              for (int i = 0; i < testCase; i++) {
                  int n = scn.nextInt();
                  String str = scn.next();
  
                  int count = 0;
                  int[] arr = new int[26];
  
                  for (int j = 0; j < n; j++) {
                      arr[(int) str.charAt(j) - 97]++;
                  }
  
                  StringBuilder ab = new StringBuilder();
                  for (int j = 0; j < 26; j++) {
                      if (arr[j] != 0) {
                          for (int j2 = 0; j2 < arr[j]; j2++) {
                              ab.append((char)(j + 97));
                          }
                      }
                  }
                  for (int j = 0; j < n; j++) {
                      if (ab.charAt(j) != str.charAt(j)) {
                          count++;
                      }
                  }
  
                  ans.append(count).append('\n');
              }
              System.out.println(ans);
          } catch (Exception e) {
              return;
          }
      }
  
      private static boolean nextPermutation(int[] array) {
          boolean hasNext = false;
          int i;
          for (i = array.length - 2; i >= 0; i--) {
              if (array[i] < array[i + 1]) {
                  hasNext = true;
                  break;
              }
          }
          if (!hasNext) {
              return false;
          }
          int j;
          for (j = i + 1; j < array.length; j++) {
              if (array[j] <= array[i]) {
                  break;
              }
          }
          j--;
          swap(array, i, j);
          reverse(array, i + 1, array.length);
          return true;
      }
  
      private static void swap(int[] array, int i, int j) {
          int temp = array[i];
          array[i] = array[j];
          array[j] = temp;
      }
  
      private static void reverse(int[] array, int start, int end) {
          for (int i = start, j = end - 1; i < j; i++, j--) {
              swap(array, i, j);
          }
      }
  }
  
  class FastScanner {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      StringTokenizer st = new StringTokenizer(" ");
  
      String next() {
          while (!st.hasMoreTokens())
              try {
                  st = new StringTokenizer(br.readLine());
              } catch (IOException e) {
                  e.printStackTrace();
              }
          return st.nextToken();
      }
  
      int nextInt() {
          return Integer.parseInt(next());
      }
  
      int[] readArray(int n) {
          int[] a = new int[n];
          for (int i = 0; i < n; i++)
              a[i] = nextInt();
          return a;
      }
  
      long nextLong() {
          return Long.parseLong(next());
      }
  }