#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

ll f(string s){
  bool f = false;
  for(int i=0;i<s.size()&&!f;i++) if(s[i]=='1') f = true;
  if(!f) return 0;
  ll l = 0, r = 0;
  for(int i=0;i<s.size();i++, l++) if(s[i]=='1') break;
  for(int i=0;i<s.size();i++, r++) if(s[s.size()-1-i]=='1') break;

  ll ocnt = 0, zcnt = 0;
  for(int i=l;i<s.size()-r;i++) (s[i]=='1'?ocnt:zcnt)++;
  if(ocnt==1) return 1;
  return 2 + zcnt;
}

int main(int argc, char const *argv[]) {
  string s;std::cin >> s;
  s += "00";
  //2個以上の0で分離
  ll ans = 0;
  string tmp = "";
  for(int i=0;i<s.size();i++){
    tmp += s[i];
    if(i!=0&&s[i]=='0'&&s[i-1]=='0'){
      ans += f(tmp);
      tmp = "";
      s[i] = '1';
    }
  }
  std::cout << ans << '\n';
  return 0;
}