#include <iostream>

using namespace std;

int main()
{
    ios::sync_with_stdio(0);

    unsigned long long maxNumberOfZeros = 0;
    unsigned long long curNumberOfZeros = 0;
    char c;
    while (cin >> c)
    {
        if(c == '0')
        {
           curNumberOfZeros++;
           if (curNumberOfZeros > maxNumberOfZeros)
            {
                maxNumberOfZeros = curNumberOfZeros;
            }
        }
        else
        {
            curNumberOfZeros = 0;
        }
    }

    if (maxNumberOfZeros % 2 == 0){
        cout << maxNumberOfZeros / 2 << endl;
    } else{
        cout << (maxNumberOfZeros + 1) / 2 << endl;
    }

    return 0;
}