#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  string s;
  cin >> s;
  int ans = 0, seq = 0;
  s.push_back('0');
  for (char c : s) {
    if (c == '1') {
      seq++;
    } else {
      if (seq > 2) ans += 2;
      else if (seq) ans += 1;
      seq = 0;
    }
  }
  cout << ans << endl;
  return 0;
}