import java.util.Scanner;

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

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

        do {
            A = sc.nextInt();
        }while (!(A>=1 && A<=20));

        do {
            B= sc.nextInt();
        }while (!(B>=1 && B<=20));

        if (A<=9 && B<=9){
            System.out.println(mult=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