import java.util.*;
import java.io.*;

class Main {

	void solve () {

		int a = in.nextInt(), b = in.nextInt();
		if (a <= 9 && b <= 9) System.out.println(a*b);
		else System.out.println(-1);
		
	}

	public static PrintWriter out = new PrintWriter(System.out);
	public static Scanner in = new Scanner(System.in);
	public static void main(String[] args) {
		new Main().solve();
		out.flush();
	}

}
/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