#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl
inline int power(int a, int b) {
    int x = 1;
    while (b) {
        if (b & 1) x *= a;
        a *= a;
        b >>= 1;
    }
    return x;
}


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

//_ ***************************** START Below *******************************

string a;

int consistency(int n, int k){

    vector<int> zeroes;
    for(int i=0; i<n; i++){
        if(a[i] == '0') zeroes.push_back(i+1);
    }

    int s = 0, e = 0;
    int l = 0;
    int ans = INF;

    while(e<zeroes.size()){


        if(e-s+1 < k+1){
            e++;
        }
        else{

            while(l<e ){
                int curr = max(zeroes[l]-zeroes[s], zeroes[e]-zeroes[l]);
                int next = max(zeroes[l+1]-zeroes[s], zeroes[e]-zeroes[l+1]);

                if(next > curr) break;
                l++;
            }
            int maxDist = max(zeroes[l]-zeroes[s], zeroes[e]-zeroes[l]);
            
            ans = min(ans, maxDist);
            s++;
            e++;
        }
    }

    return ans;
}















void solve() {
    
    int n, k;
    cin>>n >> k;

    cin >> a;
    cout << consistency(n, k) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}