import java.util.Scanner;
import java.util.stream.IntStream;

public class Main {
    public static void main(String[] arg) {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
      int B=sc.nextInt();
      if(1 <= A && A <= 9 && 1 <= B && B <= 9){
        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