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.*;
  public class Solution
  {
      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; 
          } 
      }
      //static final long mod=(long)1e9+7;
      static final long mod=998244353L;
      public static long pow(long a,long p)
      {
          long res=1;
          while(p>0)
          {
              if(p%2==1)
              {
                  p--;
                  res*=a;
                  res%=mod;
              }
              else
              {
                  a*=a;
                  a%=mod;
                  p/=2;
              }
          }
          return res;
      }
      static class Pair
      {
          int u,v;
          Pair(int u,int v)
          {
              this.u=u;
              this.v=v;
          }
      }
      /*static class Pair implements Comparable<Pair>
      {
          int v,l;
          Pair(int v,int l)
          {
              this.v=v;
              this.l=l;
          }
          public int compareTo(Pair p)
          {
              return l-p.l; 
          }
      }*/
      static long gcd(long a,long b)
      {
          if(b%a==0)
          return a;
          return gcd(b%a,a);
      }
      public static class comp implements Comparator<Pair>
      {
          public int compare(Pair p1,Pair p2)
          {
              if(p1.v>p2.v)
              return 1;
              return -1;
          }
      }
      public static void main(String args[])throws Exception
      {
          FastReader fs=new FastReader();
          PrintWriter pw=new PrintWriter(System.out);
          int tc=fs.nextInt();
          while(tc-->0)
          {
              int n=fs.nextInt();
              char c[]=fs.nextLine().toCharArray();
              char c1[]=new char[n];
              for(int i=0;i<n;i++)
              c1[i]=c[i];
              Arrays.sort(c1);
              int cnt=0;
              for(int i=0;i<n;i++)
              {
                  if(c1[i]!=c[i])
                  cnt++;
              }
              pw.println(cnt);
          }
          pw.flush();
          pw.close();
      }
  }