import java.util.*;

public class Main{
  public static void main(String[] args){
  Sccaner sc = new Scanner();
  String s = sc.next();
  
  int cnt0 = 0;
  int cnt1 = 0;
  
  for(int i=0; i<s.length(); i++){
    if( s.charAt(i) == '0')
      ++cnt0;
    else
      ++cnt1;
  }
  System.out.println(Math.min(cnt0, cnt1));
  }
}