#include<bits/stdc++.h>
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
#define ll long long 
#define vi vector < int > 
#define sz(a) ((int) (a).size())
#define ll long long 
#define ull unsigned long long
#define me(a, x) memset(a, x, sizeof(a)) 
#define eb emplace_back
#define uint unsigned int 
using namespace std;
const int N = 1e6 + 7;
char s[N];
int n, a[N];
map < vi, int > MP;
int slv(vi a) {
	while(sz(a) && !a[0]) a.erase(a.begin());
	if(!sz(a)) return 0;
	int n = sz(a) - 1;
	a[n] = 0;
	L(i, 1, n - 1) 
		if(a[i] > 1 && a[i + 1] == 0) {
			vi A, B; 
			L(j, 0, i) {
				A.emplace_back(a[j]);
			}
			L(j, i + 1, n) {
				B.emplace_back(a[j]);
			}
			return slv(A) + slv(B);
		}
	if(MP.count(a)) return MP[a];
	int ans = 0;
	vi b = a;
	R(i, n - 1, 1) 
		if(b[i - 1] > 0 && b[i] == 1) {
			if(b[i - 1] == 1 && i > 1 && b[i - 2] > 1) b[i] = 1e9, ans = slv(b);
			b = a, --b[i - 1], ++b[i + 1];
			ans = max(ans, slv(b) + 1);
			return MP[a] = ans;
		}
	return MP[a] = 0;
}

int main() {
//	freopen("input.txt","r",stdin);
	ios :: sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin >> (s + 1);
	n = strlen(s + 1);
	int cur = 0;
	L(i, 1, n) {
		if(s[i] == '1') {
			++cur;
		} else {
			a[cur] += 1;
		}
	}
	vi T(cur + 1);
	L(i, 0, cur) T[i] = a[i];
	cout << slv(T) << '\n';
	return 0;
}