import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String word = sc.next();
        String[] words = word.split("");
        int num0 = 0;
        int num1 = 0;

        for (int n = 0; n < words.length; n++) {
            if (words[n].equals("0")) {
                num0 = num0 + 1;
            }
            else {
                num1 = num1 + 1;
            }
        }
         if (num1 > num0) {
            System.out.println(num0 * 2);
        } else if (num0 > num1) {
            System.out.println(num1 * 2);
        } else {
            System.out.println(num1 + num0);
        }
    }
}
/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