import java.util.Scanner;
import java.util.Stack;

public class Main {

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

    int removals = 0;

    Stack<Character> stack = new Stack<>();
    for (char c : s.toCharArray()) {
      if (stack.empty() || stack.peek() == c)
        stack.push(c);
      else {
        stack.pop();
        removals += 2;
      }
    }

    System.out.println(removals);
  }
}
/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