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 C (GCC 5.4.1) (judge verdict: Runtime Error)

#include <stdio.h>
#include <stdlib.h>

int main(void){
	int i;
	int n;
	scanf("%d",&n);
	int a[n],b[n],c[n];
	int sum=0,plus=0;
	for(i=0;i<n;i++){
		scanf("%d",a+i);
	}
	for(i=0;i<n;i++){
		scanf("%d",b+i);
		c[i]=a[i]-b[i];
		sum=sum+c[i];
		if(c[i]>0){
			plus=plus+c[i];
		}
	}
	if(plus+sum<=0){
		printf("Yes\n");
	}else{
		printf("No\n");
	}
	
	return 0;
}