fun main(args: Array<String>) {
    agc019a()
}

fun agc019a() {
    val (q, h, s, d) = readLine()!!.split(' ').map { it.toLong() }
    val n = readLine()!!.toLong()

    val bottle1 = Math.min(Math.min(q * 4, h * 2), s)
    val bottle2 = d

    if (n == 1L) return println(bottle1)

    val answer = if (bottle1 * 2 <= bottle2) {
        bottle1 * n
    } else {
        (n / 2 * bottle2) + (if (n % 2 == 0L) 0 else bottle1)
    }

    println(answer)
}
