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: Accepted)

package main
 
import (
  "fmt"
  "os"
  "bufio"
  "strconv"
  "strings"
)

func main() {
  scanner := bufio.NewScanner(os.Stdin)
  scanner.Scan()
  stdInput := scanner.Text()
  valueList := strings.Split(stdInput, " ")
  a, _ := strconv.Atoi(valueList[0])
  b, _ := strconv.Atoi(valueList[1])
  
  if 0 < a && a < 10 && 0 < b && b < 10 {
    fmt.Println(a * b)
  } else {
    fmt.Println("-1")
  }
}