我打败了一半的人！！！！

#include <iostream>
#include <vector>
#include <string>
using namespace std;

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

    int n, m;
    string s;
    cin >> n >> m >> s;

    if (n == 1) {
        cout << 0 << endl;
        return 0;
    }
    int D = 0;
    for (int i = 0; i < n - 1; ++i) {
        if (s[i] != s[i + 1]) {
            D++;
        }
    }
    vector<int> L2;
    for (int l = 1; l < n; ++l) {
        if (s[l] == '0' && s[l - 1] == '1') {
            L2.push_back(l);
        }
    }
    vector<int> R2;
    for (int r = 0; r < n - 1; ++r) {
        if (s[r] == '1' && s[r + 1] == '0') {
            R2.push_back(r);
        }
    }
    int k2 = 0, rb = 0, la = 0;
    int i = 0, j = 0;
    while (i < L2.size() && j < R2.size()) {
        int l = L2[i], r = R2[j];
        if (l < r) {
            k2++;
            if (r > 0) rb++;
            if (l < n - 1) la++;
            i++;
            j++;
        } else {
            j++;
        }
    }
    int cntA = 0;
    if (s[0] == '0') {
        int ra = 0; 
        for (int r : R2) {
            if (r > 0) ra++;
        }
        cntA = max(0, ra - rb); 
    }
    int cntB = 0;
    if (s.back() == '1') {
        int lb = 0; 
        for (int l : L2) {
            if (l < n - 1) lb++;
        }
        cntB = max(0, lb - la); 
    }

    int k1 = cntA + cntB; 
    int use2 = min(m, k2);
    int total_reduce = use2 * 2;
    int remaining = m - use2;
    if (remaining > 0) {
        total_reduce += min(remaining, k1) * 1;
    }
    int min_degree = max(0, D - total_reduce);
    cout << min_degree << endl;

    return 0;
}