import java.util.*;

public class Main
{
	public static void main(String[] args)
    {
      	Scanner in = new Scanner(System.in);
      	String s = in.next();
      	int zer = 0, one = 0, len = s.length();
      	for (int i = 0; i < len; i++)
        	if (s.charAt(i) == '0')
            	zer++;
     	one = len-zer;
      	System.out.println(2*(int)(Math.min(zer, one)));
      	in.close();
    }
}
/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