// No.2138 Add Bacon
#include <bits/stdc++.h>

using namespace std;

int main(int argc, char *argv[])
{
	long long a, b, c, d, e;
	cin >> a >> b >> c >> d >> e;
	cout << a - b +  max(0ll, d - e) * c << endl;
	return 0;
}