/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author
 */

#include <iostream>
#include <fstream>

#ifndef SOLUTION_COMMON_H

#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using PI = pair<int, int>;
template<class T> using V = vector<T>;
using VI = V<int>;
#define _1 first
#define _2 second

#ifdef MY_DEBUG
# define DEBUG(x) x
#else
# define DEBUG(x)
#endif

template<class T>
inline void debug(T &A) {
  DEBUG(
      for (const auto &a : A) {
        cerr << a << " ";
      }
      cerr << '\n';
  )
}

template<class T, class Func>
inline void debug_with_format(T &A, Func f) {
  DEBUG(
      for (const auto &a : A) {
        cerr << f(a) << " ";
      }
      cerr << '\n';
  )
}

template<class T>
inline void debug_dim2(T &A) {
  DEBUG(
      for (const auto &as : A) {
        debug(as);
      }
  )
}

template<typename ... Args>
inline void debug(const char *format, Args const &... args) {
  DEBUG(
      fprintf(stderr, format, args ...);
      cerr << '\n';
  )
}

template<typename ... Args>
string format(const string &fmt, Args ... args) {
  size_t len = snprintf(nullptr, 0, fmt.c_str(), args ...);
  vector<char> buf(len + 1);
  snprintf(&buf[0], len + 1, fmt.c_str(), args ...);
  return string(&buf[0], &buf[0] + len);
}

template<class T1, class T2>
string fmtP(pair<T1, T2> a) {
  stringstream ss;
  ss << "(" << a._1 << "," << a._2 << ")";
  return ss.str();
}

#define SOLUTION_COMMON_H

#endif //SOLUTION_COMMON_H

const int MOD = 1000000007;

class C {
public:
  void solve(std::istream& in, std::ostream& out) {
    string S;
    in >> S;
    VI N(S.size() + 1);
    for (int i = 0; i < S.size(); ++i) {
      N[i + 1] = S[i]-'0';
    }
    debug(N);

    int ans = 0;
    function<void(int)> incr = [&](int i) {
      if (N[i] == 0) N[i] = 1;
      else {
        N[i] = 0;
        incr(i - 1);
      }
    };
    for (int i = N.size() - 1; i >= 0; --i) {
      if (i > 0 && N[i] == 1 && N[i - 1] == 1) {
        incr(i);
        ans++;
      } else if (N[i] == 1) {
        N[i] = 0;
        ans++;
      }
    }
    debug(N);

    out << ans;
  }
};


int main() {
	C solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
	return 0;
}