Problem:
Score : 300 points

Problem Statement

You've come to your favorite store Infinitesco to buy some ice tea.

The store sells ice tea in bottles of different volumes at different costs.
Specifically, a 0.25-liter bottle costs Q yen, a 0.5-liter bottle costs H yen, a 1-liter bottle costs S yen, and a 2-liter bottle costs D yen.
The store has an infinite supply of bottles of each type.

You want to buy exactly N liters of ice tea. How many yen do you have to spend?

Constraints

1 \leq Q, H, S, D \leq 10^8

1 \leq N \leq 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

Q H S D
N

Output

Print the smallest number of yen you have to spend to buy exactly N liters of ice tea.

Sample Input 1

20 30 70 90
3

Sample Output 1

150

Buy one 2-liter bottle and two 0.5-liter bottles. You'll get 3 liters for 90 + 30 + 30 = 150 yen.

Sample Input 2

10000 1000 100 10
1

Sample Output 2

100

Even though a 2-liter bottle costs just 10 yen, you need only 1 liter.
Thus, you have to buy a 1-liter bottle for 100 yen.

Sample Input 3

10 100 1000 10000
1

Sample Output 3

40

Now it's better to buy four 0.25-liter bottles for 10 + 10 + 10 + 10 = 40 yen.

Sample Input 4

12345678 87654321 12345678 87654321
123456789

Sample Output 4

1524157763907942

Solution in Go (1.14.1) (judge verdict: Accepted)

package main

import (
	"fmt"
	"sort"
)

func main() {
	var q, h, s, d, n int
	fmt.Scan(&q, &h, &s, &d, &n)

	doublePrices := []int{8 * q, 4 * h, 2 * s, d}
	sort.Ints(doublePrices)

	var ans int
	if doublePrices[0] == d && n%2 == 1 {
		if n == 1 {
			ans = doublePrices[1] / 2
		} else {
			ans = (n-1)*d/2 + doublePrices[1]/2
		}
	} else {
		ans = n * doublePrices[0] / 2
	}

	fmt.Println(ans)
}