{-# LANGUAGE TypeApplications #-}
import qualified Data.ByteString.Char8 as BS

check :: Int -> Int -> Int -> Int -> String
check a b c d =
  if x > y
  then "No"
  else "Yes"
  where
    a2 = fromIntegral a
    b2 = fromIntegral b
    c2 = fromIntegral c
    d2 = fromIntegral d
    x = ceiling $ c2 / b2
    y = ceiling $ a2 / d2

main :: IO()
main = do  
  [a,b,c,d] <- map (read @Int . BS.unpack) . BS.words <$> BS.getLine
  putStrLn $ check a b c d
