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: #include <bits/stdc++.h>
  using namespace std;
  long long int gcd(long long int a, long long int b) {
    return b ? gcd(b, a % b) : a;
  }
  long long int sqr(long long int n) { return n * n; }
  long long int mod = 1e9 + 7;
  long long int pow(long long int p, long long int d) {
    return d ? (pow((p * p) % mod, d >> 1) * (d & 1 ? p : 1)) % mod : 1ll;
  }
  vector<bool> SieveOfEratosthenes(long long int num) {
    vector<bool> soe;
    soe.assign(num + 1, true);
    soe[0] = false;
    soe[1] = false;
    for (long long int i = 2; i * i <= num; i++) {
      if (soe[i] == true) {
        for (long long int j = i * 2; j <= num; j += i) soe[j] = false;
      }
    }
    return soe;
  }
  long long int bs(vector<long long int> &v, long long int l, long long int r,
                   long long int key) {
    while (l + 1 < r) {
      long long int mid = (l + r) / 2;
      if (v[mid] > key)
        r = mid;
      else
        l = mid;
    }
    return l;
  }
  int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    long long int t;
    cin >> t;
    while (t--) {
      long long int n;
      cin >> n;
      string s;
      cin >> s;
      ;
      string k = s;
      sort(k.begin(), k.end());
      long long int cnt = 0;
      for (int i = 0; i < s.size(); ++i) {
        if (s[i] != k[i]) cnt++;
      }
      cout << cnt << '\n';
    }
  }
  