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++14 (GCC 5.4.1) (judge verdict: Runtime Error)

#include "bits/stdc++.h"
using namespace std;

typedef long long int ll;

int main()
{
    int n;cin>>n;
    int arr[n+2],brr[n+2];
    for(int i=1;i<=n;i++)
        cin>>arr[i];
    for(int i=1;i<=n;i++)
        cin>>brr[i];
    sort(arr+1,arr+n+1);
    sort(brr+1,brr+n+1);
    int a=0,b=0;
    for(int i=1;i<=n;i++)
    {
        if(arr[i]>brr[i])
            a+=arr[i]-brr[i];
        else b+=brr[i]-arr[i];
    }
    if(a%2!=b%2 || (!a&&!b))cout<< "Yes\n";
    else cout<< "No\n";


    return 0;
}