import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		String input = sc.next();
		String[] inputSplit = input.split("");
		int num0 = 0;
		for (int i = 0; i < inputSplit.length; i++) {
			if (inputSplit[i].equals("0")) {
				num0++;
			}
		}
		System.out.print(Math.min(num0, inputSplit.length - num0) * 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