import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc=new Scanner(System.in);
		
		String s=sc.next();
		int count=0;
		int ans=0;
		
		for(int i=0;i<s.length();i++) {
			if(s.charAt(i)=='0') {
				count++;
			}else {
				ans++;
			}
		}
		int r=Math.min(count,ans)*2;
		System.out.println(r);
		sc.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