import java.util.*;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        
        int A,B;

        A = sc.nextInt();
        B = sc.nextInt();

       
        if(A >= 10 || B >= 10) {
            System.out.print("-1");
        } else {
            System.out.print(A * B);
        }

        sc.close();


    }
}
/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