#include <iostream>
#include <string>
#include <cmath>

using namespace std;

void run_case(int test_case){
    int n, k;
    string s;
    
    cin >> n >> k;
    cin >> s;
    
    int result = 0;
    
    auto ti = s.end() - 1;
    int l = s.length();
    for(auto it = s.begin(); it != s.begin() + l/2; ++it){
        if((*it) != (*ti)){
            result++;
        }
        --ti;
    }
    cout << "Case #" << test_case << ": " << abs(k - result) << endl;
}



int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);

    int t;
    cin >> t;

    for(int tc = 1; tc <= t; ++tc){
        run_case(tc);
        cout << flush;
    }
}