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


signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(20);
    
    string s;
    cin>>s;
    s = "000" + s;
    int n =s.size();
    reverse(s.begin(),s.end());
    int ans = 0 ;
    for(int i=0;i<n-1;){
        if(s[i]=='1'){
            if(s[i+1]!='1'){
                i++;
                continue;
            }
            while(i < n-1 && s[i]=='1') s[i] = '0',i++;
            ans++;
            s[i] = '1';
        }
        else i++;
    }
    //cerr << s << endl;
    for(int i=0;i<n;i++){
        if(s[i]=='1') ans++;
    }
    cout << ans << endl;
}