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 seqPermute {
      static class FastReader {
          BufferedReader br;
          StringTokenizer st;
  
          public FastReader()
          {
              br = new BufferedReader(
                  new InputStreamReader(System.in));
          }
          public FastReader(String file_name)throws IOException
          {
              br = new BufferedReader(
                  new FileReader(file_name));
          }
  
          String next()
          {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  }
                  catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
  
          int nextInt() { return Integer.parseInt(next()); }
  
          long nextLong() { return Long.parseLong(next()); }
  
          double nextDouble()
          {
              return Double.parseDouble(next());
          }
  
          String nextLine()
          {
              String str = "";
              try {
                  str = br.readLine();
              }
              catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
          
          public int[] nextArray(int n){
              int ar[] = new int[n];
              for(int i=0;i<n;i++)
                  ar[i] = this.nextInt();
              return (ar);
          }
      }
  
     static class OutputWriter{
          BufferedWriter writer;
  
           public OutputWriter(OutputStream stream){
             writer = new BufferedWriter(new OutputStreamWriter(stream));
           }
  
           public OutputWriter(String file_name) throws IOException{
             writer = new BufferedWriter(new FileWriter("output.txt"));
           }
         
           public void print(int i) throws IOException {
             writer.write(i);
           }
  
           public void print(String s) throws IOException {
              writer.write(s);
            }
  
           public void print(char []c) throws IOException {
              writer.write(c);
           }
  
           public void println(int i) throws IOException {
             writer.write(i+"\n");
           }
  
           public void println(long i) throws IOException {
             writer.write(i+"\n");
           }
  
           public void println(String s) throws IOException {
              writer.write(s+"\n");
            }
  
           public void println(char []c) throws IOException {
              writer.write(c+"\n");
           }
  
           public  void close() throws IOException {
              writer.close();
           }
  
      }
      public static long gcd(long a,long b){
          return(a==0?b:gcd(b%a,a));
      }
      public static long lcm(long a,long b){
          //return (a*b)/gcd(a,b);
          //this is modified to avoid integer overflow by multiplying a*b
          return((a/gcd(a,b))*b);
      }
      public static void initialize_io_redirection()throws IOException{
          try{
              boolean MP = System.getProperty("MY_PC")!=null;
              if(MP){
                  fs = new FastReader("input.txt");
                  op = new OutputWriter("output.txt");
                  System.setOut(new PrintStream(new File("output.txt")));
              }
              else{
                  fs = new FastReader();
                  op = new OutputWriter(System.out);
              }
         }
         catch(Exception e){
              fs = new FastReader();
              op = new OutputWriter(System.out);
         }
      }
     static FastReader fs;
     static OutputWriter op;
      public static void main(String[] args)throws IOException{
          initialize_io_redirection();
          int t = fs.nextInt();
          while(t-- > 0)
              solve();
          op.close();
      }
  
      public static void solve()throws IOException{
      	int n=fs.nextInt();
      	String str = fs.nextLine();
          char []arr = str.toCharArray();
          Arrays.sort(arr);
          int c=0;
          for(int i=0;i<n;i++){
          	char ch=str.charAt(i);
          	if(arr[i]!=ch)
          		c++;
          }
          System.out.println(c);
      }
  }
  
  