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.*;
  import java.util.*;
  
   // Author : Savan Patel
  public class A implements Runnable {
  
      static class PP{
          int univ;
          int skill;
          PP(int u,int s){
              univ=u;
              skill=s;
          }
      }
  
      public void run() {
         	
          InputReader sc = new InputReader(System.in);
          PrintWriter out = new PrintWriter(System.out);
         
          int t=sc.nextInt();
          while(t-->0){
              int n=sc.nextInt();//8 7 1 3 4 2 5 
              char ch[]=sc.readString().toCharArray();
              char cc[]=ch.clone();
              Arrays.sort(cc);
              int ans=0;
              for(int i=0;i<cc.length;i++){
                  if(ch[i]!=cc[i]){
                      ans++;
                  }
              }
              out.println(ans);
          }
  
          out.close();
  
      }
   
  
  //========================================================================
  
  	
  	static void scanArray(int a[],InputReader sc)
  	{
  		for(int i=0;i<a.length;i++)
  		{
  			a[i]=sc.nextInt();
  		}
          //Arrays.sort(a);
  	}
  
  	static class pair<U extends Comparable<U>, V extends Comparable<V>> implements Comparable<pair<U, V>> {
          public U x;
          public V y;
  
          public pair(U x, V y) {
              this.x = x;
              this.y = y;
          }
  
          public int compareTo(pair<U, V> other) {
              int i = x.compareTo(other.x);
              if (i != 0) return i;
              return y.compareTo(other.y);
          }
  
          public String toString() {
              return x.toString() + " " + y.toString();
          }
  
          public boolean equals(Object obj) {
              if (this.getClass() != obj.getClass()) return false;
              pair<U, V> other = (pair<U, V>) obj;
              return x.equals(other.x) && y.equals(other.y);
          }
  
          public int hashCode() {
              return 31 * x.hashCode() + y.hashCode();
          }
  
      }
  
  
      static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private SpaceCharFilter filter;
          private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
   
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
         
          public int read() {
              if (numChars==-1)
                  throw new InputMismatchException();
             
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  }
                  catch (IOException e) {
                      throw new InputMismatchException();
                  }
                 
                  if(numChars <= 0)              
                      return -1;
              }
              return buf[curChar++];
          }
       
          public String nextLine() {
              String str = "";
              try {
                  str = br.readLine();
              }
              catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
          public int nextInt() {
              int c = read();
             
              while(isSpaceChar(c))
                  c = read();
             
              int sgn = 1;
             
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
             
              int res = 0;
              do {
                  if(c<'0'||c>'9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              while (!isSpaceChar(c));
             
              return res * sgn;
          }
         
          public long nextLong() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              long res = 0;
             
              do {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              while (!isSpaceChar(c));
                  return res * sgn;
          }
         
          public double nextDouble() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              double res = 0;
              while (!isSpaceChar(c) && c != '.') {
                  if (c == 'e' || c == 'E')
                      return res * Math.pow(10, nextInt());
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              if (c == '.') {
                  c = read();
                  double m = 1;
                  while (!isSpaceChar(c)) {
                      if (c == 'e' || c == 'E')
                          return res * Math.pow(10, nextInt());
                      if (c < '0' || c > '9')
                          throw new InputMismatchException();
                      m /= 10;
                      res += (c - '0') * m;
                      c = read();
                  }
              }
              return res * sgn;
          }
         
          public String readString() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              StringBuilder res = new StringBuilder();
              do {
                  res.appendCodePoint(c);
                  c = read();
              }
              while (!isSpaceChar(c));
             
              return res.toString();
          }
       
          public boolean isSpaceChar(int c) {
              if (filter != null)
                  return filter.isSpaceChar(c);
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
       
          public String next() {
              return readString();
          }
         
          public interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
          }
      }
  
      public static void main(String args[]) throws Exception {
          new Thread(null, new A(),"Main",1<<27).start();
      }
  }
  