#include <bits/stdc++.h>
#define loop(n) for (int ngtkana_is_genius = 0; ngtkana_is_genius < int(n); ngtkana_is_genius++)
#define rep(i, begin, end) for(int i = int(begin); i < int(end); i++)
#define all(v) v.begin(), v.end()
#define lint long long
auto cmn = [](auto& a, auto b){if (a > b) {a = b; return true;} return false;};
auto cmx = [](auto& a, auto b){if (a < b) {a = b; return true;} return false;};
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail){
  std::cerr << " " << head;
  debug_impl(tail...);
}
#define debug(...)\
  std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";\
  debug_impl(__VA_ARGS__);\
  std::cerr << std::noboolalpha;

int main() {
  std::cin.tie(0); std::cin.sync_with_stdio(false);
  std::string s; std::cin >> s;
  std::string t;
  auto x = 2, y = 0, z = 0;
  int nx = 0, ny = 0, nz = 0;
  constexpr int inf = 1'000'000'000;
  for (auto c : s) {
    t.push_back(c);
    if (c == '0') {
      nx = x + 1;
      ny = inf;
      nz = std::min({x, y, z});
    } else {
      nx = x;
      ny = std::min({x, y, z}) + 1;
      nz = inf;
    }
    cmn(nx, inf);
    cmn(ny, inf);
    cmn(nz, inf);
    std::swap(x, nx);
    std::swap(y, ny);
    std::swap(z, nz);
    // debug(x, y, z, t);
  }
  std::cout << std::min({x, y, z}) << std::endl;
  return 0;
}