#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
  string S; cin >> S; int N= (int) S.size();
  
  int head = 0; int tail = 0;
  
  string T = "";
  
  while( head < N){
    if( S[head] == '0'){ head++; tail++; T += '0';}
    else{
     while( tail < N && S[tail] == '1'){ tail++;}
     T += '1';
     head = tail;}
     } 
 

   
   N = (int) T.size();
   head = 0; tail = 0; 

   string  U = "";
   int cnt = 0;
   while( head < N){
     int res = 0;
     if( T[head] == '1'){ head++; tail++; U += '1';}
     else{
       while( tail < N && T[tail] == '0'){ res++; tail++;}
       if( res > 1){ U += '0';} else{ cnt++;}
     }
     head = tail;
   }
  
  head = 0; tail = 0; N = (int) U.size();
  while( head < N){
    if( U[tail] == '0'){ head++; tail++;}
    else{
      while( tail < N && U[tail] == '1'){ tail++;}
         cnt+= 2;}
      
      head = tail;
  }
  
  cout << cnt << endl;
     
    
  return 0;}