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;
  
  public class Solution {
  	
  	public static void merge(char[] a, int l, int m, int r) {
  		int n1 = m-l+1;
  		int n2 = r-m;
  		
  		char[] left = new char[n1];
  		char[] right = new char[n2];
  		
  		for(int i = 0; i<n1; i++) {
  			left[i] = a[i+l];
  		}
  		for(int j = 0; j<n2; j++) {
  			right[j] = a[m+j+1];
  		}
  		
  		int i = 0; int j = 0;
  		int k = l;
  		while(i<n1 && j<n2) {
  			if(left[i] < right[j]) {
  				a[k] = left[i];
  				i++;
  				k++;
  			}
  			else {
  				a[k] = right[j];
  				j++;
  				k++;
  			}
  		}
  		while(i<n1) {
  			a[k] = left[i];
  			i++;
  			k++;
  		}
  		while(j<n2) {
  			a[k] = right[j];
  			j++;
  			k++;
  		}
  		
  	}
  	
  	public static void sort(char[] sarr, int l, int r) {
  		if(l<r) {
  			int m = (l+r)/2;
  			sort(sarr, l, m);
  			sort(sarr, m+1, r);
  			merge(sarr, l, m, r);
  		}
  	}
  
  	public static void main(String[] args) throws IOException{
  		// TODO Auto-generated method stub
  		BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
  		int t = Integer.parseInt(read.readLine().split(" ")[0]);
  		for(int i = 0; i<t; i++) {
  			int n = Integer.parseInt(read.readLine().split(" ")[0]);
  			String s = read.readLine();	
  			char[] sarr = s.toCharArray();
  			sort(sarr, 0, n-1);
  			int ans = 0;
  			for(int j = 0; j<n; j++) {
  				if(s.charAt(j)==sarr[j]) {
  					ans++;
  				}
  			}
  			ans = n-ans;
  			System.out.println(ans);
  		}
  	}
  
  }