#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<queue>
#include<vector>
#include <bitset>
#include<cmath>
using namespace std;
#define INF 110000000000
#define MOD 1000000007
typedef long long ll;
typedef pair<ll,int> P;


int main(){
  ll ans=0;
  int count=0;
  string s;
  cin>>s;
  for(int i=0;i<3;i++)s.push_back('0');
  
  for(int i=0;i<(int)s.size();i++){
    
    if(s[i]=='1') count++;
    else{
      if(count==1) ans++;
      
      else if(count==0) ;
      
      else if(s[i+1]=='1'){
        ans++;
        count++;
        continue;
      }else ans+=2;
      count=0;
    }
    //cout<<i<<" "<<ans<<endl;
  }
  cout<<ans<<endl;
}