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.BigInteger;
  
      public class TestClass {
        private static int count;
        public static void main(String[] args) {
          
          Scanner sc=new Scanner(System.in);
          int t=sc.nextInt();
          
          while(t--!=0) {
            int n=sc.nextInt();
            sc.nextLine();
            String s=sc.nextLine();
            s=s.substring(0,n);
            //System.out.println(s);
            char charArray[] = s.toCharArray();
            Arrays.sort(charArray);
          
           
            int count=0;
            for(int i=0;i<s.length();i++){
                if(s.charAt(i)!=charArray[i])count++;
            }
            System.out.println(count);
  
         }
          
  
        }
        public static int  gcd(int a,int b){
          if(a==0){
            return b;
          }
          return gcd(b%a,a);
        }
        public static int removeZeros(int n){
              int res=0,pro=1;
              while(n>0){
              	int r=n%10;
              	if(r!=0){
              		res=res+r*pro;
              	    pro*=10;
              	}
              	n/=10;
              }
              //System.out.println(res);
              return res;
  
          }
  
      }
  