#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
#include <map>
#include <cmath>
#include <bitset>
#include <string>
#include <queue>
#include <stack>
#include <set>
using namespace std;

int main() {
	int a, b, c, d, e;
	cin >> a >> b >> c >> d >> e;
	int ans = a - b;
	if (e < d) ans += c * (d - e);
	cout << ans << endl;
}