import java.util.Scanner;

public class Main {

	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		char[] array = sc.next().toCharArray();
		int onecount=0;
		int zerocount=0;
		for(int i=0;i<array.length;i++) {
			if(array[i]=='1') onecount++;
			else zerocount++;
		}
		System.out.println(Math.min(zerocount,onecount)*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