import java.util.*;
public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str=sc.next();
        int red;
        int blue;
        red=str.length()-str.replaceAll("1", "").length();
        blue=str.length()-str.replaceAll("0", "").length();
        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