
readInt :: String -> Int
readInt = read

main = do
 [q,h,s,d] <- (map readInt . words) <$> getLine
 n <- readInt <$> getLine
 print $ analyze (q,h,s,d) n


analyze (q,h,s,d) n = (n `div` 2) * min_d + (n `mod` 2) * min_s
 where
  min_d = min (min_s*2) d
  min_s = min (min_h*2) s
  min_h = min (min_q*2) h
  min_q = q
