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;
  inline long long toint(string s) {
    long long v;
    istringstream sin(s);
    sin >> v;
    return v;
  }
  template <class T>
  inline string toString(T x) {
    ostringstream sout;
    sout << x;
    return sout.str();
  }
  template <class T>
  inline T sqr(T x) {
    return x * x;
  }
  const double EPS = 1e-10;
  const double PI = acos(-1.0);
  const long long INF = 4e18;
  const long long NINF = 1 - INF;
  struct POINT {
    double x;
    double y;
  };
  long long gcd(long long x, long long y) { return y ? gcd(y, x % y) : x; }
  long long lcm(long long a, long long b) { return (a / gcd(a, b)) * b; }
  long long nCr(long long n, long long r) {
    if (r * 2 > n) r = n - r;
    long long dividend = 1;
    long long divisor = 1;
    for (unsigned int i = 1; i <= r; ++i) {
      dividend *= (n - i + 1);
      divisor *= i;
    }
    return dividend / divisor;
  }
  template <class T>
  pair<T, long long> maxP(vector<T> a, long long size) {
    pair<T, long long> p;
    long long ind = 0;
    T mx = NINF;
    for (long long i = (0); i < (size); ++i) {
      if (mx < a[i]) {
        mx = a[i];
        ind = i;
      }
    }
    p.first = mx;
    p.second = ind;
    return p;
  }
  template <class T>
  pair<T, long long> minP(vector<T> a, long long size) {
    pair<T, long long> p;
    T mn = INF;
    long long ind = 0;
    for (long long i = (0); i < (size); ++i) {
      if (mn > a[i]) {
        mn = a[i];
        ind = i;
      }
    }
    p.first = mn;
    p.second = ind;
    return p;
  }
  template <class T>
  T sumL(vector<T> a, long long size) {
    T sum = 0;
    for (long long i = (0); i < (size); ++i) {
      sum += a[i];
    }
    return sum;
  }
  long long counT(vector<long long> a, long long left, long long right,
                  long long t) {
    return upper_bound(a.begin() + left, a.begin() + right, t) -
           lower_bound(a.begin() + left, a.begin() + right, t);
  }
  long long kiriage(long long a, long long b) { return a / b + (a % b != 0); }
  long long search(vector<long long> &a, long long n) {
    std::vector<long long>::iterator iter = std::find(a.begin(), a.end(), n);
    size_t index = distance(a.begin(), iter);
    return index;
  }
  int getdigit(long long n) { return log10(n) + 1; }
  vector<long long> toBinary(long long bina) {
    vector<long long> ans;
    for (long long i = 0; bina > 0; i++) {
      ans.push_back(bina % 2);
      bina = bina / 2;
    }
    return ans;
  }
  long long n, m;
  long long h, w, k;
  string s;
  vector<long long> A, B;
  map<long long, long long> p;
  long long v, e;
  int main() {
    int N;
    cin >> N;
    for (long long i = (0); i < (N); ++i) {
      long long k;
      cin >> k;
      string s;
      cin >> s;
      vector<long long> a(k);
      for (long long j = (0); j < (k); ++j) {
        a[j] = s[j];
      }
      long long ans = 0;
      sort((a).begin(), (a).end());
      for (long long j = (0); j < (k); ++j) ans += s[j] != a[j];
      cout << ans << endl;
    }
    return 0;
  }
  