#include <iostream>
#include <unordered_map>

using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
    int a, b, c, d, e;
    cin >> a >> b >> c >> d >> e;
    int umai = a;
    int cal = b;
    int max_happy = umai - cal;
    for(int i = 1; i <=c; ++i) {
        umai += d;
        cal += e;
        if (max_happy < (umai-cal)) {
            max_happy = umai-cal;
        }
    }
    cout << max_happy << endl;
}