#include <bits/stdc++.h>
using namespace std;

int main()
{
	int a, b, c, d, e;
	cin >> a >> b >> c >> d >> e;
	int tas = a;
	int cal = b;
	int ans = tas - cal;
	for(int i = 1; i <= c; i++)
	{
		tas += d;
		cal += e;
		ans = max(ans, tas - cal);
	}
	cout << ans << endl;
	return 0;
}