Problem:
Score : 100 points

Problem Statement

Having learned the multiplication table, Takahashi can multiply two integers between 1 and 9 (inclusive) together. He cannot do any other calculation.

Given are two integers A and B.

If Takahashi can calculate A \times B, print the result; if he cannot, print -1 instead.

Constraints

1 \leq A \leq 20

1 \leq B \leq 20

All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

If Takahashi can calculate A \times B, print the result; if he cannot, print -1.

Sample Input 1

2 5

Sample Output 1

10

2 \times 5 = 10.

Sample Input 2

5 10

Sample Output 2

-1

5\times 10 = 50, but Takahashi cannot do this calculation, so print -1 instead.

Sample Input 3

9 9

Sample Output 3

81

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;

namespace abc088b
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine().Split().Select(s => int.Parse(s)).ToArray();
            var ans = input.All(x => x <= 9) ? input[0] * input[1] : -1;
            Console.WriteLine(ans);
        }
    }
}