#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;

int N;
string S;

int main(){
  cin>>S;
  N=S.size();

  string T=S;
  reverse(T.begin(),T.end());

  int ans=0;
  int one=0;
  for(int i=0;i<N;i++){
      if(T[i]=='1') one++;
      else one=0;

      if(i+1<N){
          if(T[i]=='1'&&T[i+1]=='0'){
              ans++;
              if(one>1){
                  T[i+1]='1';
              }
              one=0;
          }
      }else{
          if(T[i]=='1'){
              if(one>1) ans+=2;
              else ans++;
          }
      }
  }

  cout<<ans<<endl;

  return 0;
}