#include <bits/stdc++.h>
using namespace std;
int n, m, d[105];
char x[205];
int main() {
  scanf("%d%d%s", &n, &m, x);
  d[0] = 1;
  for (int i = 0; i < n; i++)
    if (x[i] == '1' && d[i])
      for (int j = 1; j <= m; j++)
        if (x[i + j] == '1' && (!d[i + j] || d[i + j] > d[i] + 1))
          d[i + j] = d[i] + 1;
  printf("%d\n", d[n - 1] - 1);
  return 0;
}
