import java.util.Scanner;


public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		int a[] = new int[2];
		for (int i=0;i<S.length();i++) {
			a[S.charAt(i)-'0']++;
		}
		if (a[0]>a[1]) {
			System.out.println(a[1]*2);
		} else {
			System.out.println(a[0]*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