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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"bufio"
	"os"
	"strconv"
	"strings"
)

var s = bufio.NewScanner(os.Stdin)

func ScanLine() string {
	s.Scan()
	return s.Text()
}

func main() {
	p()
}

func ScanInts() (int, int) {
	str := ScanLine()
	v := strings.Split(str, " ")
	a, _ := strconv.Atoi(v[0])
	b, _ := strconv.Atoi(v[1])
	return a, b
}

func p() int {
	a, b := ScanInts()
	if a > 10 || b > 10 {
		return -1
	}
	return a * b
}