#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:256000000")
using namespace std;
const int INF = 1000001000;
const int mod = 1000 * 1000 * 1000 + 7;
const int mod9 = 1000 * 1000 * 1000 + 9;
const double PI = 3.1415926535897932;
double sqr(double first) { return first * first; };
long double sqr(long double first) { return first * first; };
long long sqr(long long first) { return first * first; };
long long sqr(int first) { return first * 1LL * first; };
long long gcd(long long a, long long b) {
  while (b) a %= b, swap(a, b);
  return a;
}
long long bpm(long long a, long long n = -2, long long m = mod) {
  n = n >= 0 ? n : m + n;
  long long r = 1;
  while (n) {
    if (n & 1) r = (r * a) % m;
    a = (a * a) % m;
    n >>= 1;
  }
  return r;
}
long long dist(long long x1, long long y1, long long x2, long long y2) {
  return sqr(x1 - x2) + sqr(y1 - y2);
}
std::ostream& operator<<(std::ostream& os, pair<int, int> p) {
  return os << "{" << p.first << " " << p.second << "}";
}
const int N = 1000006;
int get(vector<int>& sum, int l, int r, int n) {
  r = min(r, n - 1);
  return sum[r] - (l > 0 ? sum[l - 1] : 0);
}
int main() {
  int n, k;
  cin >> n >> k;
  vector<int> sum(n, 0);
  string d;
  cin >> d;
  for (int i = 0; i < n; i++) {
    sum[i] = (i ? sum[i - 1] : 0) + (d[i] == '0');
  }
  int mn = n;
  for (int i = 0; i < n; i++) {
    if (d[i] == '0') {
      int l = 0, r = n;
      while (l != r) {
        int md = (l + r) / 2;
        if (get(sum, i - md, i + md, n) <= k) {
          l = md + 1;
        } else {
          r = md;
        }
      }
      mn = min(mn, l);
    }
  }
  cout << mn << endl;
  return 0;
}
