#include <string>
#include <iostream>
#include<algorithm>
#include<string.h>
#pragma warning (disable:4996)

using namespace std;


int main()
{
	int q1, p1, q2, p2, a, sum = 0;
	double profit1, profit2;
	cin >> q1 >> p1 >> q2 >> p2 >> a;
	profit1 = p1 / q1;
	profit2 = p2 / q2;

	while (true)
	{
		if (a <= 0)
		{
			cout << sum;
			return 0;
		}
		if (profit2 < profit1)
		{
			if (abs(a - q1) > abs(a - q2))
			{
				a = a - q2;
				sum = sum + p2;
			}
			else
			{
				a = a - q1;
				sum = sum + p1;
			}
		}
		else
		{
			a = a - q1;
			sum = sum + p1;
		}

	}
}