import qualified Data.ByteString.Char8        as BS
import qualified Data.List                    as DL

solve :: Integral a => a -> a -> a -> a -> a
solve a1 b1 a2 b2 = head $ DL.dropWhile (\x -> x `mod` b1 /= b2) [a2, a2 + a1 .. 3001]

main :: IO ()
main = do
  [a1, b1, a2, b2] <- readInts
  print $ solve a1 b1 a2 b2

readInts :: IO [Int]
readInts = DL.unfoldr (BS.readInt . BS.dropSpace) <$> BS.getLine