

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

public class Main {

	public static void main(String argsw[])
	{
		Scanner scan=new Scanner(System.in);
		Stack<Integer> stk=new Stack<Integer>();
		String eg=scan.next();
		long count=0;
		stk.add(eg.charAt(0)-'0');
		for(int i=1;i<eg.length();i++)
		{
			if( !stk.isEmpty() && (eg.charAt(i)-'0')!=stk.peek())
			{
				stk.pop();
				count+=2;
			}else {
				stk.add(eg.charAt(i)-'0');
			}
		}
		System.out.println(count);
	}
}

/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