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;
  template <typename T, size_t N>
  long long SIZE(const T (&t)[N]) {
    return N;
  }
  template <typename T>
  long long SIZE(const T &t) {
    return t.size();
  }
  string to_string(const string s, long long x1 = 0, long long x2 = 1e9) {
    return '"' + ((x1 < s.size()) ? s.substr(x1, x2 - x1 + 1) : "") + '"';
  }
  string to_string(const char *s) { return to_string((string)s); }
  string to_string(const bool b) { return (b ? "true" : "false"); }
  string to_string(const char c) { return string({c}); }
  template <size_t N>
  string to_string(const bitset<N> &b, long long x1 = 0, long long x2 = 1e9) {
    string t = "";
    for (long long __iii__ = min(x1, SIZE(b)), __jjj__ = min(x2, SIZE(b) - 1);
         __iii__ <= __jjj__; ++__iii__) {
      t += b[__iii__] + '0';
    }
    return '"' + t + '"';
  }
  template <typename A, typename... C>
  string to_string(const A(&v), long long x1 = 0, long long x2 = 1e9,
                   C... coords);
  long long l_v_l_v_l = 0, t_a_b_s = 0;
  template <typename A, typename B>
  string to_string(const pair<A, B> &p) {
    l_v_l_v_l++;
    string res = "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
    l_v_l_v_l--;
    return res;
  }
  template <typename A, typename... C>
  string to_string(const A(&v), long long x1, long long x2, C... coords) {
    long long rnk = rank<A>::value;
    string tab(t_a_b_s, ' ');
    string res = "";
    bool first = true;
    if (l_v_l_v_l == 0) res += "\n";
    res += tab + "[";
    x1 = min(x1, SIZE(v)), x2 = min(x2, SIZE(v));
    auto l = begin(v);
    advance(l, x1);
    auto r = l;
    advance(r, (x2 - x1) + (x2 < SIZE(v)));
    for (auto e = l; e != r; e = next(e)) {
      if (!first) {
        res += ", ";
      }
      first = false;
      l_v_l_v_l++;
      if (e != l) {
        if (rnk > 1) {
          res += "\n";
          t_a_b_s = l_v_l_v_l;
        };
      } else {
        t_a_b_s = 0;
      }
      res += to_string(*e, coords...);
      l_v_l_v_l--;
    }
    res += "]";
    if (l_v_l_v_l == 0) res += "\n";
    return res;
  }
  void dbgm() { ; }
  template <typename Heads, typename... Tails>
  void dbgm(Heads H, Tails... T) {
    cerr << to_string(H) << " | ";
    dbgm(T...);
  }
  void FIO() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
  }
  const long long N = 2e5 + 6;
  int32_t main() {
    FIO();
    long long tc;
    cin >> tc;
    while (tc--) {
      long long n;
      cin >> n;
      string s;
      cin >> s;
      string v = s;
      sort(v.begin(), v.end());
      long long cnt = 0;
      for (long long i = 0; i < n; i++) cnt += (s[i] != v[i]);
      cout << cnt << '\n';
    }
    return 0;
  }
  