import java.util.*;

public class Main {
  public static void main(String[] args) {
    String line = new Scanner(System.in).nextLine();
    int zeros = 0;
    int ones = 0;
    for (int ix = 0; ix < line.length(); ix++) {
      if (line.charAt(ix) == '0') {
          zeros++;
        } else if (line.charAt(ix) == '1') {
          ones++;
        }
    }
    
    System.out.println(2 * Math.min(zeros, ones));
  }
}

/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