import java.util.*;

class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);

    String s = sc.next();
    int countZero = 0, countOne = 0;

    for (int i = 0; i < s.length(); i++) {
      if (s.charAt(i) == '0')
        countZero++;
      else
        countOne++;
    }
    System.out.println(countZero > countOne ? countOne*2 : countZero*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