import Data.List

main :: IO ()
main = do
	[n, p] <- map read . words <$> getLine
	h <- map read . words <$> getLine
	print $ solve h p

solve :: [Int] -> Int -> Int
solve x p = minPair $ foldl' f (0, p) $ zip x (tail x)
	where
		f :: (Int, Int) -> (Int, Int) -> (Int, Int)
		f (dp0, dp1) (h0, h1) = (v0, v1)
			where
				v0 = min (dp0 + max 0 (h1 - h0)) (dp1 + p)
				v1 = min (dp1 + max 0 (h0 - h1)) (dp0 + p)

minPair :: (Int, Int) -> Int
minPair (x, y) = min x y