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.FileInputStream;
  import java.io.FileOutputStream;
  import java.io.PrintStream;
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.StringTokenizer;
  import static java.lang.Math.max;
  import static java.lang.Math.min;
  import static java.lang.Math.abs;
  import java.util.Arrays;
  public class JustForFunDoNotMindMe{
  	public static void main(String[] args){
  		// FileInputOutput input=new FileInputOutput("input.txt","output.txt");
  		FastReader read=new FastReader();
  	   int t=read.nextInt();
         while(t-->0){
          int  n=read.nextInt();
          char[] orr=read.next().toCharArray();;
          char[] dup=new char[orr.length];
          System.arraycopy(orr,0,dup,0,orr.length);
          Arrays.sort(dup);
          int k=0;
          for(int i=0;i<n;i++){
              if(orr[i]!=dup[i])
                  k++;
  
          }
          System.out.println(k);
         }
  		
  		
  	}//main
     
  static class FastReader {
          BufferedReader br;
          StringTokenizer st;
  
          public FastReader()
          {
              br = new BufferedReader(
                      new InputStreamReader(System.in));
          }
  
          String next()
          {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  }
                  catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
          char nextChar()
          {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  }
                  catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken().charAt(0);
          }
  
          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;
          }
   }//Fast Reader
  }//JustForFun
  class FileInputOutput{
  	FileInputStream one;
  	FileOutputStream two;
  	PrintStream three;
  	FileInputOutput(String input,String output){
  	try{
  		one=new FileInputStream(input);
  		two=new FileOutputStream(output);
  		three=new PrintStream(two);
  		System.setIn(one);
  		System.setOut(three);
  	}catch(Exception e){
  		e.printStackTrace();
  	}
  
  
  	}//cons
  }//FileInputOutput
  