#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

int x(string &m, int n, int o) {
    int p = 0, q = 0, r = 0;

    for (int s = 0; s < n; s++) {
        if (m[s] == '0') q++;
        while (q > o) {
            if (m[p] == '0') q--;
            p++;
        }
        r = max(r, s - p + 1);
    }
    return r;
}

int main() {
    int a;
    cin >> a;

    while (a--) {
        int b, c;
        string d;
        cin >> b >> c >> d;

        cout << x(d, b, c) << endl;
    }

    return 0;
}