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.lang.*;
  import java.io.*;
  
  public class Main
  {
      static long mod = (int)1e9+7;
      public static void main (String[] args) throws java.lang.Exception
      {
          FastReader sc =new FastReader();
  
          int t=sc.nextInt();
     
       // int t=1;
     
          while(t-->0)
          {
              int n=sc.nextInt();
              String s=sc.next();
              char a[]=s.toCharArray();
              for(int i=0;i<n;i++)
              {
                  for(int j=0;j<n;j++)
                  {
                      if(a[i]<a[j])
                      {
                          char temp=a[i];
                          a[i]=a[j];
                          a[j]=temp;
                      }
                  }
              }
              int count=0;
              for(int i=0;i<n;i++)
              {
                  char ch=s.charAt(i);
                  if(a[i]!=ch)
                      count++;
              }
              System.out.println(count);
          }
      }
  
  
  
  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());
          }
         
          float nextFloat()
          {
              return Float.parseFloat(next());
          }
   
          String nextLine()
          {
              String str = "";
              try {
                  str = br.readLine();
              }
              catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
         
          int[] readArray(int n) {
  int[] a=new int[n];
  for (int i=0; i<n; i++) a[i]=nextInt();
  return a;
  }
  
  long[] readArrayLong(int n) {
  long[] a=new long[n];
  for (int i=0; i<n; i++) a[i]=nextLong();
  return a;
  }
  
      }
     
      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 HashMap<Integer, Integer> sortByValue(HashMap<Integer, Integer> hm)
      {
          // Create a list from elements of HashMap
          List<Map.Entry<Integer, Integer> > list =
                 new LinkedList<Map.Entry<Integer, Integer> >(hm.entrySet());
   
          // Sort the list
          Collections.sort(list, new Comparator<Map.Entry<Integer, Integer> >() {
              public int compare(Map.Entry<Integer, Integer> o1,
                                 Map.Entry<Integer, Integer> o2)
              {
                  return (o1.getValue()).compareTo(o2.getValue());
              }
          });
           
          // put data from sorted list to hashmap
          HashMap<Integer, Integer> temp = new LinkedHashMap<Integer, Integer>();
          for (Map.Entry<Integer, Integer> aa : list) {
              temp.put(aa.getKey(), aa.getValue());
          }
          return temp;
      }
      static int DigitSum(int n)
      {
          int r=0,sum=0;
          while(n>=0)
          {
              r=n%10;
              sum=sum+r;
              n=n/10;
          }
          return sum;
      }
  }