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.math.*;
  import java.util.*;
  
  public class Main {
  
      static final int MAX_N = 1000010;
      static final int INF = 0x3f3f3f3f;
      static final int mod = 1000000007;
  
  
      public static void main(String[] args) throws IOException {
          initReader(System.in);
  
  
          int T = nextInt();
          for (int i = 1; i <= T; i++)
          solve();
  
  
          pw.flush();
      }
  
  
      /*******************************************************************************************************************************/
  
  
      public static void solve() throws IOException {
          int n = nextInt();
          char[] s = next().toCharArray();
          char[] ss = new char[n];
  
          System.arraycopy(s, 0, ss, 0, n);
  
          Arrays.sort(s);
  
          int ans = 0;
          for (int i = 0; i < n; i++) if (s[i] != ss[i]) ans++;
          pw.println(ans);
      }
  
      static class Pair {
          char x;
          int y;
  
          Pair (char x, int y) {
              this.x = x;
              this.y = y;
          }
      }
  
      /*******************************************************************************************************************************/
  
  
      /*******************************************************************************************************************************/
  
      static BufferedReader reader;
      static StringTokenizer tokenizer;
      static PrintWriter pw;
  
      public static void initReader(InputStream input) throws IOException {
          reader = new BufferedReader(new InputStreamReader(input));
          tokenizer = new StringTokenizer("");
          pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
  
  //        reader = new BufferedReader(new FileReader("test.in"));
  //        tokenizer = new StringTokenizer("");
  //        pw = new PrintWriter(new BufferedWriter(new FileWriter("test1.out")));
      }
  
      public static boolean hasNext() {
          try {
              while (!tokenizer.hasMoreTokens()) {
                  tokenizer = new StringTokenizer(reader.readLine());
              }
          } catch (Exception e) {
              return false;
          }
          return true;
      }
  
      public static String next() throws IOException {
          while (!tokenizer.hasMoreTokens()) {
              tokenizer = new StringTokenizer(reader.readLine());
          }
          return tokenizer.nextToken();
      }
  
      public static String nextLine() {
          try {
              return reader.readLine();
          } catch (Exception e) {
              return null;
          }
      }
  
      public static int nextInt() throws IOException {
          return Integer.parseInt(next());
      }
  
      public static long nextLong() throws IOException {
          return Long.parseLong(next());
      }
  
      public static double nextDouble() throws IOException {
          return Double.parseDouble(next());
      }
  
      public static char nextChar() throws IOException {
          return next().charAt(0);
      }
  
      public static short nextShort() throws IOException {
          return Short.parseShort(next());
      }
  
  }
  
  