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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>

void boubleSort(long int x[4]) {
  for (int i = 0; i < 3; i++) {
    for ( int j = 0; j < 3-i; j++) {
      if (x[j] > x[j+1]) {
        int tmp = x[j];
        x[j] = x[j+1];
        x[j+1] = tmp;
      }
    }
  }
}

int main(void) {
  long int Q, H, S, D, N;
  scanf("%ld %ld %ld %ld", &Q, &H, &S, &D);
  scanf("%ld", &N);
  
  long int values[4] = {8*Q, 4*H, 2*S, D};
  boubleSort(values);
  long int a, b, c, d;   //a<b<c<d 2L単位の値段
  a = values[0];
  b = values[1];
  c = values[2];
  d = values[3];
  
  //8Q, 4H, 2Sが最安値なら全てそれで購入できる
  if (a != D) printf("%ld", (N*a)/2);
  else {
    //Dが最安値ならできるだけDで買い、最後の1Lのみどれかで買う
    printf("%ld", (N/2)*a+(N%2)*b/2);
  }
  
  return 0;
}