#include <assert.h>
#include <limits.h>
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <complex>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using ll = long long;
using P = std::pair<ll, ll>;

#define rep(i, a, b) for (ll(i) = (a); i < (b); i++)
#define all(i) i.begin(), i.end()
#define debug(i) std::cerr << "debug "<< i << std::endl

// const ll MOD = 998244353;
const ll MOD = 1e9 + 7;

int main() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  //問題文中の添え字が0-indexか1-indexか確認!

  std::string s;
  std::cin>>s;

  ll n=s.size(),ans=0,cnt=0;

  for(ll i=n-1;i>=0;i--){
    if(s[i]=='0'){
      if(cnt>=2){
        ans++;
        cnt=1;
      }else{
        ans+=cnt;
        cnt=0;
      }
    }else{
      cnt++;
    }
  }

  if(cnt>=2)ans+=2;
  else ans+=cnt;

  std::cout<<ans;
  

  return 0;
}