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.*;
  import java.awt.geom.*;
  
  import static java.lang.Math.*;
  
  public class Solution implements Runnable {
  
  	long mod1 = (long) 1e9 + 7;
  	int mod2 = 998244353;
  
  	public void solve() throws Exception {
  		int t = sc.nextInt();
  		while (t-- > 0) {
  			int n=sc.nextInt();
  			char arr[] = sc.nextToken().toCharArray();
  			char brr[] = arr.clone();
  			int count=0;
  			Arrays.parallelSort(brr);
  			for(int i=0;i<n;i++) {
  				if(arr[i]!=brr[i]) count++;
  			}
  			out.println(count);
  
  		}
  
  	}
  
  	static long gcd(long a, long b) {
  		if (a == 0)
  			return b;
  		return gcd(b % a, a);
  	}
  
  	static void sort(int[] a) {
  		ArrayList<Integer> l = new ArrayList<>();
  		for (int i : a)
  			l.add(i);
  		Collections.sort(l);
  		for (int i = 0; i < a.length; i++)
  			a[i] = l.get(i);
  	}
  
  	static long ncr(int n, int r, long p) {
  		if (r > n)
  			return 0l;
  		if (r > n - r)
  			r = n - r;
  
  		long C[] = new long[r + 1];
  
  		C[0] = 1;
  
  		for (int i = 1; i <= n; i++) {
  
  			for (int j = Math.min(i, r); j > 0; j--)
  				C[j] = (C[j] + C[j - 1]) % p;
  		}
  		return C[r] % p;
  	}
  
  	void sieveOfEratosthenes(boolean prime[], int size) {
  		for (int i = 0; i < size; i++)
  			prime[i] = true;
  
  		for (int p = 2; p * p < size; p++) {
  			if (prime[p] == true) {
  				for (int i = p * p; i < size; i += p)
  					prime[i] = false;
  			}
  		}
  	}
  
  	static int LowerBound(int a[], int x) { // smallest index having value >= x
  		int l = -1, r = a.length;
  		while (l + 1 < r) {
  			int m = (l + r) >>> 1;
  			if (a[m] >= x)
  				r = m;
  			else
  				l = m;
  		}
  		return r;
  	}
  
  	static int UpperBound(int a[], int x) {// biggest index having value <= x
  		int l = -1, r = a.length;
  		while (l + 1 < r) {
  			int m = (l + r) >>> 1;
  			if (a[m] <= x)
  				l = m;
  			else
  				r = m;
  		}
  		return l + 1;
  	}
  
  	public long power(long x, long y, long p) {
  		long res = 1;
  		// out.println(x+" "+y);
  		x = x % p;
  		if (x == 0)
  			return 0;
  
  		while (y > 0) {
  			if ((y & 1) == 1)
  				res = (res * x) % p;
  			y = y >> 1;
  			x = (x * x) % p;
  		}
  		return res;
  	}
  
  	static Throwable uncaught;
  
  	BufferedReader in;
  	FastScanner sc;
  	PrintWriter out;
  
  	@Override
  	public void run() {
  		try {
  			in = new BufferedReader(new InputStreamReader(System.in));
  			out = new PrintWriter(System.out);
  			sc = new FastScanner(in);
  			solve();
  		} catch (Throwable uncaught) {
  			Solution.uncaught = uncaught;
  		} finally {
  			out.close();
  		}
  	}
  
  	public static void main(String[] args) throws Throwable {
  		Thread thread = new Thread(null, new Solution(), "", (1 << 26));
  		thread.start();
  		thread.join();
  		if (Solution.uncaught != null) {
  			throw Solution.uncaught;
  		}
  	}
  
  }
  
  class FastScanner {
  
  	BufferedReader in;
  	StringTokenizer st;
  
  	public FastScanner(BufferedReader in) {
  		this.in = in;
  	}
  
  	public String nextToken() throws Exception {
  		while (st == null || !st.hasMoreTokens()) {
  			st = new StringTokenizer(in.readLine());
  		}
  		return st.nextToken();
  	}
  
  	public int nextInt() throws Exception {
  		return Integer.parseInt(nextToken());
  	}
  
  	public int[] readArray(int n) throws Exception {
  		int[] a = new int[n];
  		for (int i = 0; i < n; i++)
  			a[i] = nextInt();
  		return a;
  	}
  
  	public long nextLong() throws Exception {
  		return Long.parseLong(nextToken());
  	}
  
  	public double nextDouble() throws Exception {
  		return Double.parseDouble(nextToken());
  	}
  
  }