Problem: 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.

Examples

Input

8 6


Output

16


Input

3 3


Output

-1

Solution (in JAVA):

Solution:
import java.util.*;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int x = Integer.parseInt(sc.next());
        int y = Integer.parseInt(sc.next());
        sc.close();

        // 主処理
        long num = x * 2;
        long result = -1;
        if (x % y != 0) {
            while (num % y == 0) {
                num += x;
            }
            result = num;
        }

        // 出力
        System.out.println(result);
    }
}