import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		char s[] =  scan.next().toCharArray();
		int zeroCount = 0;
		int oneCount = 0;

		for(int i = 0; i < s.length; i++) {
			if(s[i] == '0') {
				zeroCount++;
			}else {
				oneCount++;
			}
		}
		
		System.out.println(2 * Math.min(zeroCount, oneCount));
		
	}
}
/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