import java.util.*;

public class Main {
	
	public static void main(String[] args)  {
		Scanner scan = new Scanner(System.in);
		String s=scan.next();
		int len=s.length();
		int count_0=0;
		int count_1=0;
		for (int i=0;i<len;++i) {
			if(s.charAt(i)=='0')++count_0;
			if(s.charAt(i)=='1')++count_1;
		}
		System.out.print(Math.min(count_0,count_1)*2);
}
}
//end

/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