#include <bits/stdc++.h>
#define FOR(i, n) for(int i = 0; i < (n); ++i)
#define REP(i, a, b) for(int i = (a); i < (b); ++i)
#define TRAV(i, a) for(auto &i : (a))
#define SZ(x) ((int)(x).size())
#define X first
#define Y second
#define PR std::pair
#define MP std::make_pair
typedef long long ll;
typedef std::vector<int> VI;
typedef std::pair<int, int> PII;

int main(){
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);

	std::string s;
	std::cin >> s;
	int max = 0;
	int have = 0;
	TRAV(i, s){
		if(i == '1') max = std::max(max, have), have = 0;
		else have++;
	}

	std::cout << (max+1)/2 << "\n";

	return 0;
}