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

#define FOR(i, a, b) for (int i=(a); i<(b); i++)

const int maxN = 1 << 20;

char T[maxN];

int main()
{
	scanf ("%s", T);
	int n = strlen(T), last = 0, res = 0;
	FOR(i, 1, n) if (T[i] == '1')
	{
		res = max(res, i - last - 1);
		last = i;
	}
	res = (res + 1) / 2;
	printf("%d\n", res);
	
	return 0;	
}