import Data.List

toInt :: String -> Int
toInt = read :: String -> Int

myCeiling :: Int -> Int -> Int
myCeiling x y = ceiling ((fromIntegral x) / (fromIntegral y))

main = do
  [a, b, c, d] <- map toInt . words <$> getLine
  putStrLn $ if myCeiling a d >= myCeiling c b then "Yes" else "No"
