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: Wrong Answer)

#include <stdio.h>
 
int main(void){
 
int x,y,ans;
int i;
int check = 0;
int ans_2;
 
 scanf("%d",&x);
scanf("%d",&y);
 
if(x == y)
printf("-1");
 
for(i=1;i<10000000;i++){
ans = x * i;
ans_2 = ans%y ;
if(ans_2  != 0){
printf("%d",ans);
check = 1;
goto end;
}
}
end:
if(check == 0)
printf("-1");
 
return 0;
}