module Main where


eval :: Int -> Int -> Int -> [Int] -> Int
eval _ _ _ [] = 0
eval t d x (y:ys) = eval t d x ys + if abs (x - y) `mod` d == 0
                      then abs (x - y) `div` d
                      else 2 * t + 1

main :: IO ()
main = do
        [_, d, t] <- fmap (map read . words) getLine
        xs <- fmap (map read . words) getLine
        print $ eval t d (head xs) (tail xs) + 2 * t + 1