#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  string s; cin >> s;
  int n = s.size();
  int z = 0, o = 0;
  int res = 0;
  V<> v;
  for (int i = 0; i < n; ++i) {
    if (s[i] == '0') {
      ++z, o = 0;
    } else {
      ++o, z = 0;
    }
    if (s[i] == s[i + 1]) continue;
    if (o) {
      v.push_back(o);
      if (i + 2 >= n or s[i + 2] == '0') {
        if (count(begin(v), end(v), 1) == (int)v.size()) {
          res += v.size();
        } else {
          res += v.size() + 1;
        }
        V<>().swap(v);
      }
    }
  }
  cout << res << '\n';
}