import qualified Data.ByteString.Char8  as C
import Data.List

main = sol <$> get >>= print

get = fmap (unfoldr (C.readInt . C.dropWhile (==' '))) . C.lines <$> C.getContents

sol [[_,a,b],xs] = sum . fmap (min b . (*a)) $ zipWith (-) (tail xs) xs
