#include <bits/stdc++.h>   using namespace std;   int main() {     string s;     vector<int> v;     int n, d, p = 0, cnt = 0, mx = -1;     cin >> n >> d >> s;     for (int i = 0; i < n; i++)       if (s[i] ==  1 ) v.push_back(i);     for (int i = 1; i < v.size(); i++) {       if (v[i] - v[i - 1] > mx) mx = v[i] - v[i - 1];     }     if (mx > d) {       cout << -1;       return 0;     }     while (p < n - 1) {       p += d;       while (s[p] ==  0 ) p--;       cnt++;     }     cout << cnt;     return 0;   }   