{-# LANGUAGE Strict #-}

main :: IO ()
main = do
  [a, b, c, d] <- map read . words <$> getLine
  putStrLn $ if solve a b c d then "Yes" else "No"

solve :: Int -> Int -> Int -> Int -> Bool
solve a b c d = x >= y
  where x = ceilDiv a d
        y = ceilDiv c b

ceilDiv :: Int -> Int -> Int
ceilDiv a b = (a + b - 1) `div` b
