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.IOException;
  import java.io.InputStream;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.InputMismatchException;
  import java.util.List;
  
  public class SubsequencePermutation {
  	static StringBuilder output = new StringBuilder();
  
  	public static void main(String[] args) {
  		int t = ni();
  		while (t > 0) {
  			t--;
  			int length = ni();
  			String listChar = ns();
  			List<Integer> numbers = new ArrayList<>();
  			List<Integer> newNumbers = new ArrayList<>();
  			for (char temp : listChar.toCharArray()) {
  				numbers.add((int) temp);
  			}
  			newNumbers.addAll(numbers);
  			Collections.sort(newNumbers);
  			int count = 0;
  			for (int i = 0; i < length; i++) {
  				if (newNumbers.get(i) != numbers.get(i)) {
  					count++;
  				}
  			}
  			output.append(count).append("\n");
  		}
  		System.out.println(output);
  	}
  
  	static InputStream is = System.in;
  	static byte[] inbuf = new byte[1 << 24];
  	static int lenbuf = 0, ptrbuf = 0;
  
  	static int readByte() {
  		if (lenbuf == -1)
  			throw new InputMismatchException();
  		if (ptrbuf >= lenbuf) {
  			ptrbuf = 0;
  			try {
  				lenbuf = is.read(inbuf);
  			} catch (IOException e) {
  				throw new InputMismatchException();
  			}
  			if (lenbuf <= 0)
  				return -1;
  		}
  		return inbuf[ptrbuf++];
  	}
  
  	static boolean isSpaceChar(int c) {
  		return !(c >= 33 && c <= 126);
  	}
  
  	static int skip() {
  		int b;
  		while ((b = readByte()) != -1 && isSpaceChar(b))
  			;
  		return b;
  	}
  
  	static double nd() {
  		return Double.parseDouble(ns());
  	}
  
  	static char nc() {
  		return (char) skip();
  	}
  
  	static String ns() {
  		int b = skip();
  		StringBuilder sb = new StringBuilder();
  		while (!(isSpaceChar(b))) {
  			sb.appendCodePoint(b);
  			b = readByte();
  		}
  		return sb.toString();
  	}
  
  	static char[] ns(int n) {
  		char[] buf = new char[n];
  		int b = skip(), p = 0;
  		while (p < n && !(isSpaceChar(b))) {
  			buf[p++] = (char) b;
  			b = readByte();
  		}
  		return n == p ? buf : Arrays.copyOf(buf, p);
  	}
  
  	static int ni() {
  		int num = 0, b;
  		boolean minus = false;
  		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
  			;
  		if (b == '-') {
  			minus = true;
  			b = readByte();
  		}
  		while (true) {
  			if (b >= '0' && b <= '9') {
  				num = num * 10 + (b - '0');
  			} else {
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  
  	static long nl() {
  		long num = 0;
  		int b;
  		boolean minus = false;
  		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
  			;
  		if (b == '-') {
  			minus = true;
  			b = readByte();
  		}
  		while (true) {
  			if (b >= '0' && b <= '9') {
  				num = num * 10 + (b - '0');
  			} else {
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  }
  