import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        char[] chars = s.next().toCharArray();
        ArrayList<Integer> list = new ArrayList<>();
        for (char c : chars) {
            list.add(Character.getNumericValue(c));
        }

        int zero = 0;
        int one = 0;
        for (int num : list) {
            if (num == 0) zero++;
            else one++;
        }
        System.out.println(Math.min(zero, one) * 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