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

using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vvi = vector<vi>;

#define f(i,a,b) for(int i = (a); i < (b); i++)
#define pb emplace_back
#define PB push_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define dump(x) cout << #x << "=" << x << endl;

signed main()
{
	//ios_base::sync_with_stdio(0);
	//cin.tie(0);

	string s;
	cin >> s;
	//dump(s);
	int m, cm;
	m = 0;
	cm = 0;
	f(i,0,sz(s))
	{
		if(s[i] == '0')
			cm++;
		else
			cm = 0;
		m = max(m,cm);
	}
	int out = m/2;
	if(m%2)
		out++;
	cout << out;
	


	return 0;
}