import Control.Monad
import Data.Maybe
import Data.List
import qualified Data.ByteString.Char8 as BS

main = abc164b

abc164b = do
    [a, b, c, d] <- getIntList
    putStrLn $
        let aoki = divMod c b
            taka = divMod a d
         in if uncurry (+) aoki > uncurry (+) taka
            then "No"
            else "Yes"

readInt = fst . fromJust . BS.readInteger
readIntList = map readInt . BS.words
getIntList = readIntList <$> BS.getLine