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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>

int main(void)
{
    int a;
    scanf("%d",&a);
    if(a%2 == 0 ||a%3 == 0||a%5 == 0||a%7 == 0){
        if(a/1 < 10 || a/2 < 10 || a/3 < 10 || a/4 < 10 || a/5 < 10 || a/6 < 10 || a/7 < 10 || a/8 < 10 || a/9 < 10) printf("YES");
        else printf("NO");
    }
    else{
        printf("NO");    
    }
    return 0;
}