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.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.Scanner;
  import java.util.StringTokenizer;
  import java.io.*;
  import java.util.*;
  import java.text.DecimalFormat;
  import java.math.*;
  
  public class Main {
  
  static int  mod = 1000000007;
  /*****************code By Priyanshu *******************************************/ 
  
      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();
          }
  
          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;
          }
      }
      // this > other return +ve
      // this < other return -ve
      // this == other return 0
       public static class Pair implements Comparable<Pair> {
        long st;
        long et;
  
        public Pair(long st, long et) {
           this.st = st;
           this.et = et;
        }
  
        public int compareTo(Pair other) {
           if (this.st != other.st) {
              return (int)(this.st - other.st);
           } else {
              return (int)(this.et - other.et);
           }
        }
     }
  
      static long fastPower(long a, long b, int n) {
              
              long res = 1;
              
              while ( b > 0) {
                  
                  if ( (b&1) != 0) {
                      res = (res * a % n) % n;
                  }
                  
                  a = (a % n * a % n) % n;
                  b =  b >> 1;
              }
              
              return res;
              
          }
  
       // function to find
      // the rightmost set bit
      static int PositionRightmostSetbit(int n)
      {
          // Position variable initialize
          // with 1 m variable is used to
          // check the set bit
          int position = 1;
          int m = 1;
   
          while ((n & m) == 0) {
   
              // left shift
              m = m << 1;
              position++;
          }
          return position;
      }
      
           // used for swapping ith and jth elements of array
        // public static void swap(int[] arr, int i, int j) {
        //   int temp = arr[i];
        //   arr[i] = arr[j];
        //   arr[j] = temp;
        // }
          public static void swap(long i, long j) {
          long temp = i;
          i = j;
          j = temp;
        }
  
  
      static boolean palindrome(String s) {
          return new StringBuilder(s).reverse().toString().equals(s);
      }
      
    static boolean isPerfectSquare(double x)
      {
              double sr = Math.sqrt(x);
              return ((sr * sr) == x);     
      }
  
  
   public static long gcd(long a, long b)
      {
        if (b == 0)
          return a;
        return gcd(b, a % b);
      }
      
     
  
     static int nod(long l) {
         if(l>=1000000000000000000l) return 19;
         if(l>=100000000000000000l) return 18;
         if(l>=10000000000000000l) return 17;
         if(l>=1000000000000000l) return 16;
         if(l>=100000000000000l) return 15;
         if(l>=10000000000000l) return 14;
         if(l>=1000000000000l) return 13;
         if(l>=100000000000l) return 12;
         if(l>=10000000000l) return 11;
         if(l>=1000000000) return 10;
         if(l>=100000000) return 9;
         if(l>=10000000) return 8;
         if(l>=1000000) return 7;
         if(l>=100000) return 6;
         if(l>=10000) return 5;
         if(l>=1000) return 4;
         if(l>=100) return 3;
         if(l>=10) return 2;
         return 1;
      }
        //Arrays.sort(a,(c,d) -> Integer.compare(c[0],d[0]));
  
      
      public static boolean areAllBitsSet(int n )
      {
          // all bits are not set
          if (n == 0)
              return false;
       
          // if true, then all bits are set
          if (((n + 1) & n) == 0)
              return true;
       
          // else all bits are not set
          return false;
      }
  
       public static long[] sort(long[] arr) {
          List<Long> temp = new ArrayList();
          for (long i : arr) temp.add(i);
          Collections.sort(temp);
          int start = 0;
          for (long i : temp) arr[start++] = i;
          return arr;
      }
     
   
  
          public static int[] radixSort2(int[] a)
      {
          int n = a.length;
          int[] c0 = new int[0x101];
          int[] c1 = new int[0x101];
          int[] c2 = new int[0x101];
          int[] c3 = new int[0x101];
          for(int v : a) {
              c0[(v&0xff)+1]++;
              c1[(v>>>8&0xff)+1]++;
              c2[(v>>>16&0xff)+1]++;
              c3[(v>>>24^0x80)+1]++;
          }
          for(int i = 0;i < 0xff;i++) {
              c0[i+1] += c0[i];
              c1[i+1] += c1[i];
              c2[i+1] += c2[i];
              c3[i+1] += c3[i];
          }
          int[] t = new int[n];
          for(int v : a)t[c0[v&0xff]++] = v;
          for(int v : t)a[c1[v>>>8&0xff]++] = v;
          for(int v : a)t[c2[v>>>16&0xff]++] = v;
          for(int v : t)a[c3[v>>>24^0x80]++] = v;
          return a;
      } 
  
    
  
  
   
  
  
      public static void main(
          String[] args)
      {
          try {
              System.setIn(new FileInputStream("input.txt"));
              System.setOut(new PrintStream(new FileOutputStream("output.txt")));
          } catch (Exception e) {
              System.err.println("Error");
          }
           
         FastReader sc = new FastReader();
          int t = Integer.parseInt(sc.next());
        // int t = 1;
         // StringBuilder ans = new StringBuilder();
          
     while(t-->0){
          int n = sc.nextInt();
        //  long k = sc.nextLong();
  
          char a[] = sc.next().toCharArray();
  
          char b[] = new char[a.length];
  
          for(int i = 0;i<a.length;i++){
                  b[i] = a[i];
          }
  
          Arrays.sort(a);
  
              int c = 0;
           for(int i = 0;i<a.length;i++){
                  if(b[i] != a[i]){
                      c++;
                  }
          }
  
          System.out.println(c);
  
  
  
  
          
             
      }
    }
  }
  //code By Priyanshu 
  