#include <bits/stdc++.h>

using namespace std;

#define pb push_back
#define sqr(x) ((x) * (x))
#define fi first
#define se second

typedef pair<int, int> ii;

const int OO = 1e9 + 7;

int Exp2(int a) {
    int res = 1;
    for (int i = 0; i < a; i++) res *= 2;
    return res;
}

int search_first_zero(vector<int> v) {
    for (int i = 0; i < v.size(); i++)  {
        if (v[i] == 0)
            return i;
    }
    return -1;
}

void Inp()
{
    string s;
    cin >> s;
    vector<int> n;

    if (s[0] == '0') {
        cout << -1 << endl;
        return;
    }
    for (char c : s) {
        if (c == '1') {
            n.push_back(1);
        } else if (c == '0') {
            n.push_back(0);
        }
    }
    int ret = 0;
    while (count(n.begin(), n.end(), 1) < n.size()) {
        int steps = search_first_zero(n);
        if (steps == -1)
            break;

        ret += 1;
        vector<int> m = n;
        //cout << count(n.begin(), n.end(), 1) << endl;
        for (int i = 0; i < n.size() - steps; i++) {
            m[i + steps] = max(n[i], n[i + steps]);
        }
        n = m;
        steps *= 2;
    }
    cout << ret << endl;
}

int main()
{
    ios_base::sync_with_stdio(false); cin.tie(nullptr);
    Inp();
    return 0;
}