/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.17 17:19:39
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    string s;cin >> s;
    bool c = false;
    int cnt = 0;
    for (int i = s.size()-1; i >= 0; i--) {
        if (c && s[i] == '1') {
            s[i] = '0';
        }
        else if (c) {
            c = false;
            s[i] = '1';
            i++;
        }
        else if (s[i] == '1' && i > 0 && s[i-1] == '1') {
            c = true;
            s[i] = '0';
            cnt++;
        }
    }
    for (int i = 0; i < s.size(); i++) {
        if (s[i] == '1') cnt++;
    }
    if (s[0] == '0') cnt++;
    cout << cnt << endl;
    return 0;
}