#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int solve(string& s) {
    reverse(s.begin(), s.end());
    int cnt = 0;
    int ans = 0;
    int n = s.size();
    bool f = false;
    for (int i = 0; i < n; i++) {
        char c = s[i];
        if (c == '0') {
            if (cnt > 0) {
                ans++;
                if (cnt > 1 || f) {
                    f = true;
                }
            } else {
                ans += f;
                f = false;
            }
            cnt = 0;
        } else {
            cnt++;
        }
    }
    cnt += f;
    ans += min(cnt, 2);
    return ans;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    string s;
    cin >> s;
    cout << solve(s) << endl;
    return 0;
}