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.util.*;
  import java.io.*;
  import java.math.*;
  import java.math.BigInteger;
  /**
   *
   * @author alanl
   */
  public class Main{
      static BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
      static StringTokenizer st;
      static PrintWriter pr = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
      static Integer[][]arr;
      static int ans = -1;
      public static void main(String[] args) throws IOException {
          int t = readInt();
          while(t-->0){
              int n = readInt();
              String s = readLine();
              char[]arr = s.toCharArray();
              Arrays.sort(arr);
              int ans = 0;
              for(int i = 0; i<n; i++){
                  if(arr[i]!=s.charAt(i))ans++;
              }
              println(ans);
          }
      }
      static String next () throws IOException {
          while (st == null || !st.hasMoreTokens())
                  st = new StringTokenizer(input.readLine().trim());
          return st.nextToken();
      }
      static long readLong () throws IOException {
          return Long.parseLong(next());
      }
      static int readInt () throws IOException {
          return Integer.parseInt(next());
      }
      static double readDouble () throws IOException {
          return Double.parseDouble(next());
      }
      static char readChar () throws IOException {
          return next().charAt(0);
      }
      static String readLine () throws IOException {
          return input.readLine().trim();
      }
      static void print(Object b) {
          System.out.print(b);
      }
      static void println(Object b) {
          System.out.println(b);
      }
      static void println() {
          System.out.println();
      }
  }
  