import Control.Applicative
import Control.Monad
import Data.List

main :: IO ()
main = do
    [q, h, s, d] <- fmap read . words <$> getLine :: IO [Int]
    n <- readLn :: IO Int
    let bp2 = minimum [q * 8, h * 4, s * 2, d]
    let ans = case () of
            _ | bp2 == q * 8 -> n * 4 * q
              | bp2 == h * 4 -> n * 2 * h
              | bp2 == s * 2 -> n * s
              | bp2 == d, even n -> (n `div` 2) * d
              | otherwise ->
                    (n `div` 2) * d + minimum [q * 4, h * 2, s]
    print ans