#include <stdio.h>

int main(){

    int x = 0, t;

    scanf("%d", &t);

    while(x < t){
        int n;

        scanf("%d", &n);
        char p[n+10];
        scanf("%s", &p);
        int count = 0;

        if(n <= 1){
            printf("%d\n", count);
        }

        if(n > 1){
            for(int i = 0; i < n/2; i++){
                for (int j = n-1; j >= n/2; j--){
                    if(i != j){
                        if(p[i] == p[j]){
                            count++;
                        }
                    }
                }
            }
            if(n % 2 == 0){
                printf("%d\n", count*2);
            }
            else{
                printf("%d\n", count*2 + 2);
            }
        }



        x++;
    }

    return 0;
}