module Main where

import Control.Monad

main :: IO ()
main = do
    [x, y] <- fmap read . words <$> getLine :: IO [Double]
    _ <- getLine
    as <- fmap read . words <$> getLine :: IO [Double]
    let f (a, b) = if a * y / x > b then True else False
    if any f (zip as (tail as))
        then putStrLn "NO"
        else putStrLn "YES"