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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

class Main {

    public static void main(String[] args) throws IOException {
        ReaderA.init(System.in);
        long x = ReaderA.nextLong();
        long y = ReaderA.nextLong();
        if (x % y == 0) System.out.println(-1);
        else System.out.println(x);
    }
}

/**
 * Reader class based on the article at "https://www.cpe.ku.ac.th/~jim/java-io.html"
 */
class ReaderA {
    private static BufferedReader reader;
    private static StringTokenizer tokenizer;

    static void init(InputStream inputStream) {
        reader = new BufferedReader(new InputStreamReader(inputStream));
        tokenizer = new StringTokenizer("");
    }

    static String next() throws IOException {
        String read;
        while (!tokenizer.hasMoreTokens()) {
            read = reader.readLine();
            if (read == null || read.equals(""))
                return "-1";
            tokenizer = new StringTokenizer(read);
        }

        return tokenizer.nextToken();
    }

    static int nextInt() throws IOException {
        return Integer.parseInt(next());
    }

    static long nextLong() throws IOException {
        return Long.parseLong(next());
    }

    //    Get a whole line.
//    static String line() throws IOException {
//        return reader.readLine();
//    }
//
//    static double nextDouble() throws IOException {
//        return Double.parseDouble(next());
//    }
}