import java.util.Scanner;

public class Main{
  public static void main(String[] args){
	  Scanner sc = new Scanner(System.in);
	  String s=sc.next();
	  int r=0,b=0;
	  for(int i=0;i<s.length();i++) {
		  if(s.substring(i, i+1).equals("0"))r++;
		  else b++;
	  }
	  System.out.println(Math.min(r, b)*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