import java.util.Scanner;

class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		int cnt_zero = 0, cnt_one = 0;
		for(int i = 0; i < S.length(); i++) {
			if(S.charAt(i) == '0') cnt_zero++;
			else cnt_one++;
		}
		System.out.println(2 * Math.min(cnt_zero, cnt_one));
	}
}
/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