import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int m = sc.nextInt();
        int n = sc.nextInt();
        int result = getCM(m, n);
        System.out.println(result);
    }

    public static int getCM(int m, int n){
        int max=Math.max(m,n);
        for (int i = max; i <= m*n; i++) {
            if(i%m==0&&i%n==0){
                return i;
            }
        }
        return -1;
    }
}