main :: IO ()
main = do
  [q,h,s,d] <- map read.words <$> getLine :: IO [Int]
  n <- read <$> getLine :: IO Int
  let minEven = minimum [8*q,4*h,2*s,d]
      minOdd = minimum [4*q,2*h,s]
  print $ (n`div`2)*minEven + if odd n then minOdd else 0
