import java.util.*;
import static java.lang.System.*;

public class Main{

public static void main(String args[]){

Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    
    if(A<=9){
        if(B<=9){
        out.println(A*B);
        }else
        out.println("-1");
        }else
        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