import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		//List<String> list= new ArrayList<String>(Arrays.asList(s.split("")));
		//List<Integer> list=new ArrayList<Integer>();
		//Long[] array = new Long[6];
		String s = sc.next();
		List<String> list= new ArrayList<String>(Arrays.asList(s.split("")));
		int zero = 0;
		int one = 0;
		for(int i=0;list.size()>i;i++) {
			if(list.get(i).equals("0"))
				zero++;
			else
				one++;
		}
		if(zero>=one)
			System.out.println(one*2);
		else
			System.out.println(zero*2);
	}
}
/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