import java.util.*;

public class Main {

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

}


/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