#include <bits/stdc++.h>
using namespace std;

int main()
{
  string s;
  cin >> s;
  int z = 0;
  int zmax = -1;
  for(size_t i = 0; i < s.size(); ++i)
  {
    if(s[i] == '1')
      zmax = max(z,zmax), z = 0;
    else
      z++;
  }
  cout << (zmax+1)/2 << endl;
}