import java.util.*;
import java.io.*;

public class Main{
 public static void main(String[] args){
 Scanner s = new Scanner(System.in);
   String str = s.nextLine();
   int k =0;
   
   for(int i=0; i<str.length(); i++){
    if(str.charAt(i)=='0'){
    k++;
    }
   }
  System.out.print(2*Math.min(k, (int)str.length()-k));
   
 }
  
  
}
/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