import java.util.*;
public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  String po=sc.next();
  int length=po.length();
  String p=po.replace("1","");
  po=po.replace("0","");
  System.out.println(Math.min(p.length(),po.length())*2);
}
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz