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

int main(void){
    string S; cin >> S;
    S += '0';
    vector<pair<int, pair<int, int>>> n;
    
    int cnt = 0;
    int s;
    int t;
    int l = 0;
    for (int i = 0; i < S.length(); i++) {
        if (S[i] == '1') {
            if (l == 0) s = i;
            l++;
        } else {
            if (l > 0) {
                t = i-1;
                n.push_back({l, {s, t}});
            }
            l = 0;
        }
    }
    
    long long ans = 0;
    for (int i = n.size() - 1; i >= 0; i--) {
        auto p = n[i];
        int l = p.first;
        int s = p.second.first;
        int t = p.second.second;
        if (l == 1) {
            ans++;
        } else if (i != 0 && n[i-1].second.second + 2 == s) {
            ans++;
            n[i-1].first++;
            n[i-1].second.second++;
        } else {
            ans += 2;
        }
    }
    cout << ans << endl;
}