import Control.Applicative
import Control.Monad
import qualified Data.ByteString.Char8 as B
import Data.Maybe (fromJust)
import Text.Printf
import Debug.Trace

main = do
  [h,w,n,k] <- fmap (read :: String -> Integer) . words <$> getLine
  putStrLn $ if (h+w-2) `mod` n  == k-1 then "YES" else "NO"