main = do
    xs <- (map read . words) <$> getLine :: IO [Int]
    let a = xs !! 0
        b = xs !! 1
        c = xs !! 2
        d = xs !! 3
    let x = (c - 1) `div` b + 1
        y = (a - 1) `div` d + 1
    if x <= y then putStrLn "Yes"
              else putStrLn "No"