#include <bits/stdc++.h>
using namespace std;
int main() {
    string tmp;
    cin>>tmp;
    int l_zeros = 0;
    int longest_zeros = 0;
    bool bordered = false;
    for(auto i =0; i < tmp.size(); i++){
        if(tmp[i] =='0'){
            l_zeros++;
        }
        else{
            if(!bordered && l_zeros){
                longest_zeros = l_zeros;
            }
            else if(bordered && ceil(l_zeros/2.)>longest_zeros){
                longest_zeros = ceil(l_zeros/2.);
            }
            l_zeros = 0;
            bordered = true;
        }
    }
    //check right border
    if(tmp[tmp.size()-1] == '0' && l_zeros>= longest_zeros){
        longest_zeros = l_zeros;
    }
        cout<<longest_zeros<<endl;

    return 0;
}
//10100110101
//1000010010001