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.io.*;
  import java.util.*;
  public class GlobalR15A {
      public static void main(String[] args) {
          JS scan = new JS();
          int tt = scan.nextInt();
          while(tt-->0){
              int n = scan.nextInt();
              char[] s= scan.next().toCharArray();
              char[] s1 = s.clone();
              Arrays.sort(s1);
              int count = 0;
              int[] left = new int[26];
              int[] right =new int[26];
              Arrays.fill(left,-1);
              Arrays.fill(right,-1);
              for(int i = 0;i<s.length;i++){
                  if(left[s1[i]-'a']==-1)left[s1[i]-'a'] = i;
                  if(i==s.length-1){
                      right[s1[i]-'a'] = i;
                  }else if(i<s.length-1 && s1[i+1]!=s1[i]){
                      right[s1[i]-'a'] = i;
                  }
              }
              for(int i = 0;i<s.length;i++){
                  if(i<left[s[i]-'a'] ||i>right[s[i]-'a']){
                      count++;
                      //System.out.println(i+" "+s[i]);
                  }
              }
              System.out.println(count);
          }
      }
      static class JS {
          public int BS = 1 << 16;
          public char NC = (char) 0;
          byte[] buf = new byte[BS];
          int bId = 0, size = 0;
          char c = NC;
          double num = 1;
          BufferedInputStream in;
  
          public JS() {
              in = new BufferedInputStream(System.in, BS);
          }
  
          public JS(String s) throws FileNotFoundException {
              in = new BufferedInputStream(new FileInputStream(new File(s)), BS);
          }
  
          public char nextChar() {
              while (bId == size) {
                  try {
                      size = in.read(buf);
                  } catch (Exception e) {
                      return NC;
                  }
                  if (size == -1) return NC;
                  bId = 0;
              }
              return (char) buf[bId++];
          }
  
          public int nextInt() {
              return (int) nextLong();
          }
  
          public long nextLong() {
              num = 1;
              boolean neg = false;
              if (c == NC) c = nextChar();
              for (; (c < '0' || c > '9'); c = nextChar()) {
                  if (c == '-') neg = true;
              }
              long res = 0;
              for (; c >= '0' && c <= '9'; c = nextChar()) {
                  res = (res << 3) + (res << 1) + c - '0';
                  num *= 10;
              }
              return neg ? -res : res;
          }
  
          public double nextDouble() {
              double cur = nextLong();
              return c != '.' ? cur : cur + nextLong() / num;
          }
  
          public String next() {
              StringBuilder res = new StringBuilder();
              while (c <= 32) c = nextChar();
              while (c > 32) {
                  res.append(c);
                  c = nextChar();
              }
              return res.toString();
          }
  
          public String nextLine() {
              StringBuilder res = new StringBuilder();
              while (c <= 32) c = nextChar();
              while (c != '\n') {
                  res.append(c);
                  c = nextChar();
              }
              return res.toString();
          }
  
          public boolean hasNext() {
              if (c > 32) return true;
              while (true) {
                  c = nextChar();
                  if (c == NC) return false;
                  else if (c > 32) return true;
              }
          }
      }
  }
  