#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    string s;
    cin >> s;
    int n = s.size();

    int r = 0;
    for (int i = n - 1; i >= 0; i--) {
        if (s[i] == '1') {
            r++;
            if (i > 0 && s[i - 1] == '1') {
                while (i >= 0 && s[i] == '1') i--;
                if (i < 0) {
                    r++;
                    break;
                }
                s[i] = '1';
                i++;
            }
        }
    }

    cout << r << endl;

    return 0;
}