import           Data.Ratio as R

main :: IO ()
main = do [_n, k, x, y] <- map read . words <$> getLine
          a <- map read . words <$> getLine
          print $ solve k (x, y) a

solve :: Int -> (Int, Int) -> [Int] -> Int
solve k (x, y) a = solve' a'
    where a' = filter (> 0) $ map (\i -> ceiling $ (i - 1) R.% k) a

          solve' :: [Int] -> Int
          solve' [] = 0
          solve' a''
            | x * length a'' <= y = sum a'' * x
            | otherwise = y * m + solve' a'''
            where m = minimum a''
                  a''' = filter (> 0) $ map (\i -> i - m) a''