The Monster

Description
A monster is chasing after Rick and Morty on another planet. They’re so frightened that sometimes they scream. More accurately, Rick screams at times b, b + a, b + 2a, b + 3a, … and Morty screams at times d, d + c, d + 2c, d + 3c, ….

The Monster will catch them if at any point they scream at the same time, so it wants to know when it will catch them (the first time they scream at the same time) or that they will never scream at the same time.
Input
The first line of input contains two integers a and b (1 ≤ a, b ≤ 100).
The second line contains two integers c and d (1 ≤ c, d ≤ 100).

Output
Print the first time Rick and Morty will scream at the same time, or  - 1 if they will never scream at the same time.

Sample Input

Input
20 2
9 19

Output
82

Input
2 1
16 12

Output
-1

#include"iostream"
#include"string.h"
using namespace std;

int main()
{
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    bool ai[1000000];
    memset(ai,0,sizeof(ai));
    bool sign=false;
    for(int i=b;i<1000000;i+=a)
    {
        ai[i]=true;
    }

    int res;
    for(int i=d;i<1000000;i+=c)
    {
        if(ai[i])
        {
            res=i;
            sign=true;
            break;
        }
        ai[i]=true;
    }

    if(sign)
    {
        cout<else
    cout<<"-1"<return 0;
}