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

    return 0;
}