import java.util.*;

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

       Scanner ab = new Scanner(System.in);

		int a= ab.nextInt();
		int b= ab.nextInt();
        
        if((a<=9)&&(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