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;
  string to_string(char c) { return "'" + string(1, c) + "'"; }
  string to_string(string s) { return '"' + s + '"'; }
  string to_string(bool f) {
    if (f)
      return "True";
    else
      return "False";
  }
  string to_string(const char *s) { return to_string((string)s); }
  template <typename A>
  string to_string(A);
  template <typename A, typename B>
  string to_string(pair<A, B> p) {
    return "(" + to_string(p.first) + ": " + to_string(p.second) + ")";
  }
  template <typename A>
  string to_string(A v) {
    bool f = false;
    string r = "{";
    for (auto x : v) {
      if (f) r += ", ";
      r += to_string(x);
      f = true;
    }
    return r += "}";
  }
  template <typename A>
  string to_string(vector<vector<A>> v) {
    string r;
    for (auto x : v) r += "\n" + to_string(x);
    return r;
  }
  long long Nerr;
  template <typename A>
  string to_string(A *p) {
    return to_string(vector<A>(p, p + Nerr));
  }
  void err(istream_iterator<string>) { cerr << '\n'; }
  template <typename T, typename... Args>
  void err(istream_iterator<string> it, T a, Args... args) {
    cerr << *it << " = " << to_string(a) << "; ";
    err(++it, args...);
  }
  template <typename T>
  void kek(T ans) {
    cout << ans << '\n';
    exit(0);
  }
  signed main() {
    ios_base::sync_with_stdio(0);
    long long TESTS = 1;
    cin >> TESTS;
    while (TESTS--) {
      long long n;
      cin >> n;
      string s;
      cin >> s;
      string t = s;
      sort((t).begin(), (t).end());
      long long diff = 0;
      for (long long i = 0; i < (long long)s.size(); i++)
        if (s[i] != t[i]) diff++;
      cout << diff << '\n';
    }
  }
  