#include "bits/stdc++.h"

typedef long long int ll;

using namespace std;



int main() {

    string myInput;

    cin >> myInput;

    ll max = 0;

    ll counter = 0;
    for (ll i = 0; i  < (ll)myInput.size(); ++i){

        if ( myInput[i] == '1') {
            if (counter > max){
                max = counter;
            }
            counter = 0;
        }
        else
            counter++;

    }

    cout << ceil (max/2.0) << endl;

    return 0;
}