import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.nio.Buffer;
import java.util.Scanner;

public class Rivers {

    public static void main(String[] args) {
        //BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        Scanner input = new Scanner(System.in);
        String test = input.nextLine();
        System.out.println(minDays(test));

    }

    private static int minDays(String input) {
        int minimum = 0;
        int length = 0;
        String[] nuly = input.split("1");
        for (String zeros : nuly) {
            if (zeros.length() > length) {
                length = zeros.length();
            }
        }
        if (length % 2 == 0) {
            minimum = length / 2;
        } else {
            minimum = length / 2 + 1;
        }
        return minimum;
    }
}