import java.util.*;

public class Main {
    public static void main(String args[] ) throws Exception {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int reds = 0;
        int idx = 0;

        while (idx < s.length()) {
            if (s.charAt(idx++) == '0') reds++;
        }
        System.out.println(Math.min(reds, s.length()-reds) * 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