private fun readInts() = readLine()!!.split(" ").map { it.toInt() }.toList()

fun main(args: Array<String>) {
    val (Q, H, S, D) = readInts()
    var N = readLine()!!.toLong()

    val single = setOf(4 * Q, 2 * H, S).min()!!
    val double = setOf(D, 2 * single).min()!!

    var ans = 0L
    while (N >= 2) {
        ans += double
        N -= 2
    }

    if (N == 1L) {
        ans += single
    }

    println(ans)
}