main.java

import java.util.*;

public class main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        if(!sc.hasNextInt()) return;

        int T = sc.nextInt();
        while(T-->0){
            int n = sc.nextInt();
            String s = sc.next();
            int res=0;
            boolean inDiscord = false;
            for (int i = 0; i < n/2; i++) {
                if(s.charAt(i)!=s.charAt(n-1-i)){
                    if(!inDiscord){
                        res++;
                        inDiscord = true;
                    }
                }else{
                    inDiscord = false;
                }
            }
            System.err.println(res);
        }
    }
}