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.sql.Array;
  import java.text.DateFormat;
  import java.text.ParseException;
  import java.text.SimpleDateFormat;
  import java.time.Instant;
  import java.util.*;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  
  public class Main {
      public static class Node implements Comparable<Node> {
          int my;
          int oth;
          Node(int my,int oth) {
              this.my = my;
              this.oth = oth;
          }
  
          @Override
          public int compareTo(Node o) {
              return ((o.oth - o.my) - (this.oth - this.my));
          }
      }
  
      public static class Point implements Comparable<Point>{
          int i;
          int j;
          Point(int i, int j) {
              this.i = i;
              this.j = j;
          }
  
          @Override
          public int compareTo(Point o) {
              return this.i - o.i;
          }
      }
  
      static long inverse(int n,int MD) {
          return n == 1 ? 1 : inverse(n - MD % n, MD) * (MD / n + 1) % MD;
      }
  
      static long choose(int n, int k, int MD) {
          return k == 0 ? 1 : choose(n - 1, k - 1, MD) * n % MD * inverse(k, MD) % MD;
      }
  
      /************************ SOLUTION STARTS HERE ************************/
      private static void solve() {
          int t = nextInt();
  
          while(t-- > 0) {
              int n = nextInt();
              String s = nextLine();
              String[] orig = s.split("");
              String[] arr = s.split("");
              Arrays.sort(arr);
  
              int cnt = 0;
              for(int i=0;i<n;i++)
                  if(!arr[i].equals(orig[i])) cnt++;
  
              println(cnt);
          }
      }
  
  
      /************************ SOLUTION ENDS HERE ************************/
  
  
  
      /************************ TEMPLATE STARTS HERE **********************/
  
      public static void main(String[] args) throws IOException, ParseException {
          reader = new BufferedReader(new InputStreamReader(System.in));
          writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)), false);
          st = null;
          solve();
          reader.close();
          writer.close();
      }
  
      static BufferedReader  reader;
      static PrintWriter     writer;
      static StringTokenizer st;
  
      static String next() {
          while (st == null || !st.hasMoreTokens()) {
              try {
                  String line = reader.readLine();
                  if (line == null) {
                      return null;
                  }
                  st = new StringTokenizer(line);
              } catch (Exception e) {
                  throw new RuntimeException();
              }
          }
          return st.nextToken();
      }
  
      static String nextLine() {
          String s = null;
          try {
              s = reader.readLine();
          } catch (IOException e) {
              e.printStackTrace();
          }
          return s;
      }
  
      static int nextInt() {
          return Integer.parseInt(next());
      }
  
      static long nextLong() {
          return Long.parseLong(next());
      }
  
      static double nextDouble() {
          return Double.parseDouble(next());
      }
  
      static char nextChar() {
          return next().charAt(0);
      }
  
      static int[] nextIntArray(int n) {
          int[] a = new int[n];
          int i = 0;
          while (i < n) {
              a[i++] = nextInt();
          }
          return a;
      }
  
      static long[] nextLongArray(int n) {
          long[] a = new long[n];
          int i = 0;
          while (i < n) {
              a[i++] = nextLong();
          }
          return a;
      }
  
      static int[] nextIntArrayOneBased(int n) {
          int[] a = new int[n + 1];
          int i = 1;
          while (i <= n) {
              a[i++] = nextInt();
          }
          return a;
      }
  
      static long[] nextLongArrayOneBased(int n) {
          long[] a = new long[n + 1];
          int i = 1;
          while (i <= n) {
              a[i++] = nextLong();
          }
          return a;
      }
  
      static void print(Object o) {
          writer.print(o);
      }
  
      static void println(Object o) {
          writer.println(o);
      }
  
      static void printArr(int[] arr) {
          for(int i = 0 ; i < arr.length; i++)
              System.out.print(arr[i] + " ");
          System.out.println();
      }
  
      public static void exchange(int[] arr, int i, int j) {
          int temp = arr[i];
          arr[i] = arr[j];
          arr[j] = temp;
      }
  
      public static void shuffle(int arr[], int n) {
          for (int i = 0; i < n; i++) {
              int r = (int)Math.floor(Math.random() * (i+1));
              exchange(arr, i, r);
          }
      }
  
      /************************ TEMPLATE ENDS HERE ************************/
  }
  