#include <bits/stdc++.h>

using namespace std;

void test_case(int tc){
    int n, k;
    cin >> n >> k;

    vector<bool> strip;

    int blacks = 0;
    int whites = 0;
    for(int i = 0; i < k; ++i){
        char c;
        cin >> c;

        if(c == 'B'){
            blacks++;
            strip.push_back(true);
        } else{
            whites++;
            strip.push_back(false);
        }
    }

    int min_whites = whites;

    for(int i = 0; i < n - k; ++i){
        char c;
        cin >> c;

        if(strip[i]){
            blacks--;
        } else {
            whites--;
        }

        if(c == 'B'){
            blacks++;
            strip.push_back(true);
        } else {
            whites++;
            strip.push_back(false);
        }

        min_whites = min(min_whites, whites);
    }

    cout << min_whites << '\n';
}



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

    int t;
    cin >> t;

    for(int tc = 1; tc <= t; ++tc){
        test_case(tc);
    }

    cout << flush;

    return 0;
}