#include <iostream>
#include <math.h>

using namespace std;

int main() {
  
  ios_base::sync_with_stdio(false);
  
  char c;
  int max = 0;
  int m = 0;
  while( (c = cin.get()) != '\n' ) {
    if (c == '1') {
      if ( m > max ) {
        max = m;
      }
      m = 0;
    }
    else if (c == '0') {
      m++;
    }    
  }
  
  cout << ceil(max/2.0) << endl;
  
  
  return 0;
}