#include <bits/stdc++.h>
using namespace std;
const long long int N = 1e5;
long long int t[N];
string s;
long long int n, k;
bool chek(long long int x) {
  for (long long int i = 0; i < n; i++) {
    if (!(s[i] - '0')) {
      long long int en = i + x;
      long long int st = i - x;
      en = min(en, n - 1);
      st = max((long long int)0, st);
      long long int cur = t[en] - (st ? t[st - 1] : 0) - 1;
      if (cur >= k) return true;
    }
  }
  return false;
}
int32_t main() {
  ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cin >> n >> k;
  cin >> s;
  long long int x = 0;
  for (long long int i = 0; i < s.size(); i++) {
    if (!(s[i] - '0')) x++;
    t[i] = x;
  }
  long long int l = -1, r = n + 1;
  while (r - l > 1) {
    long long int mid = (r + l) / 2;
    if (chek(mid))
      r = mid;
    else
      l = mid;
  }
  cout << r;
}
