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