import java.util.Scanner;
 
public class Main {
 
    public static void main(String[] args) {
        int n,m,i,j,k,p,q,o,l,s,tt=1,t,z,aa,r=0;
        Scanner sc= new Scanner(System.in);
        n=sc.nextInt();
        m=sc.nextInt();
        if(n>9 || m>9)
        {
            System.out.println(-1);
        }
        else
        {
            System.out.println(n*m);
        }
 
    }
}
/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