
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final Scanner scanner = new Scanner(System.in);
        final char[] cubes = scanner.nextLine().toCharArray();

        int zeroCounter = 0;
        int oneCounter = 0;
        for (final char cube : cubes) {
            if (cube == '1') {
                oneCounter++;
            } else {
                zeroCounter++;
            }
        }

        System.out.println(2 * Math.min(zeroCounter, oneCounter));
    }
}

/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