import java.util.*;
class Main{
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		char[] s=sc.next().toCharArray();
		
		int count1=0,count0=0;
		for(char c:s){
			if(c=='1')
				count1++;
			else
				count0++;
		}
		
		System.out.println(Math.min(count0,count1)*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