#include <bits/stdc++.h>
using namespace std;

int main(){
    string veze;
    vector<long long> priestor;
    long long counter=0; 
    pair<long long, long long> mx = {0, 0};  // cislo index

    cin >> veze;

    for (int i=1; i<veze.size(); i++){
        if (veze[i] == '0'){
            counter ++;
        }
        else if (veze[i] == '1' && veze[i-1] != '1'){
            priestor.push_back(counter);
            if (counter > mx.first){
                mx.first = counter;
                mx.second = priestor.size()-1;
            }
            counter = 0;
        }
    }
    priestor[mx.second] = (priestor[mx.second]+1) / 2;
    mx.first = 0;
    // cout >> max(priestor.begin(), priestor.end());
    for (int i=1; i<priestor.size(); i++){
        if (priestor[i] > mx.first) mx.first = priestor[i];
    }

    cout << mx.first << endl;
}