import java.util.*;
import java.util.Arrays;

public class Main{
        public static void main(String[] args){
                Scanner scan = new Scanner(System.in);
                String src = scan.next();
                String Array[] = src.split("");
                List<String> list = Arrays.asList(Array);

                int count0 = Collections.frequency(list, "0");
                int count1 = Collections.frequency(list, "1");

                if(count0 > count1){
                        System.out.println(count1*2);
                }else{
                        System.out.println(count0*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