#include <iostream>
#include <math.h>

using namespace std;

int main(int argc, char const *argv[])
{
    int c;
    int max=0, count=0;
    c = getchar();
    while (c == '1' || c=='0')
    {
        if (c == '0')
            ++count;
        else if(c=='1'){
            if(max < count)
                max = count;
            count = 0;
        }
        c = getchar();
    }
    cout << ceil(max/2.0) << endl;
    return 0;
}