import java.awt.*;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.math.BigInteger;
import java.util.*;
import java.util.List;

public class Main {

    static String br = System.getProperty("line.separator");
    static Scanner sc = new Scanner(System.in);
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) {
        int A = nextInt();
        int B = nextInt();

        if(A>9 || B>9) println("-1");
        else println(A*B);
    }

    static int nextInt() {
        return Integer.parseInt(next());
    }

    static Long nextLong() {
        return Long.parseLong(next());
    }

    static String next() {
        return sc.next();
    }

    static String nextLine(){
        return sc.nextLine();
    }

    static void println(Object o) {
        out.println(o);
        out.flush();
    }

    static void print(Object o) {
        PrintWriter out = new PrintWriter(System.out);
        out.print(o);
        out.flush();
    }
}

/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