#include <bits/stdc++.h>
using namespace std;
bool com(string a, string b) {
  if (a.size() == b.size()) {
    return (a < b);
  }
  return (a.size() < b.size());
}
int main() {
  string s;
  cin >> s;
  string curr = "1";
  int ans = 0;
  while (com(curr, s)) {
    ans++;
    curr = curr + "00";
  }
  cout << ans << endl;
  return 0;
}
