import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    char[] S = scanner.next().toCharArray();
    int c0 = 0;
    int c1 = 0;
    for (char c : S) {
      if (c == '0') c0++;
      else c1++;
    }
    System.out.println(Math.min(c0, c1) * 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