The Monster

给出$a,b,c,d$ 四个数，两个人在尖叫，第一个人在b,b+a,b+2a,b+3a......时刻尖叫，第二个人在d,d+c,d+2c,d+3c......时刻尖叫，问他们第一次在相同时刻尖叫是什么时候。 如果他们永远不可能同时尖叫，请输出 `-1`。

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.

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 $ ).

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

20 2
9 19

82

2 1
16 12

-1

In the first sample testcase, Rick's $ 5 $ th scream and Morty's $ 8 $ th time are at time $ 82 $ . In the second sample testcase, all Rick's screams will be at odd times and Morty's will be at even times, so they will never scream at the same time.