#!/usr/bin/perl6
use strict;
use warnings;
use 5.010;
 
 
my $line1 = <>;
chomp($line1);
my @ab = split(" ",$line1);
my $a = $ab[0];
my $b = $ab[1];
 
my $line2 = <>;
chomp($line2);
my @cd = split(" ",$line2);
my $c = $cd[0];
my $d = $cd[1];
 
my $output = -1;
 
OUTERLOOP: for(my $i = $b; $i < 10000; $i += $a)
{
  for(my $j = $d; $j < 10000; $j += $c)
  {
    if($i == $j)
    {
      $output = $i;
      last OUTERLOOP;
    }
  }
}
 
say $output;
 

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