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

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int A = Integer.parseInt(sc.next());
        int B = Integer.parseInt(sc.next());
        sc.close();

        if (A<10 && B<10) {
            System.out.println(A*B);
        } else {
            System.out.println("-1");
        }
    }
}

/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