Problem:
Score : 100 points

Problem Statement

You are given positive integers X and Y.
If there exists a positive integer not greater than 10^{18} that is a multiple of X but not a multiple of Y, choose one such integer and print it.
If it does not exist, print -1.

Constraints

1 ≤ X,Y ≤ 10^9

X and Y are integers.

Input

Input is given from Standard Input in the following format:

X Y

Output

Print a positive integer not greater than 10^{18} that is a multiple of X but not a multiple of Y, or print -1 if it does not exist.

Sample Input 1

8 6

Sample Output 1

16

For example, 16 is a multiple of 8 but not a multiple of 6.

Sample Input 2

3 3

Sample Output 2

-1

A multiple of 3 is a multiple of 3.

Solution in JavaScript (node.js v5.12) (judge verdict: Accepted)

"use strict";
const Main = (input) =>{
   let xs = input.trim().split(' ').map(v=>parseInt(v,10));
   let X = xs[0];
   let Y = xs[1];
   let ans = 0;
     if(X%Y==0){
       ans = -1;
     }else{
       ans = X;
     }
    console.log(ans);
}
Main(require('fs').readFileSync('/dev/stdin','utf8'));