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

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