#include <bits/stdc++.h>
using namespace std;
int main() {
    // Input
    int A, B, C, D, E;
    cin >> A >> B >> C >> D >> E;

    // All Search
    int ans = INT_MIN;
    for (int i = 0; i <= C; ++i) ans = max(ans, (A + D * i) - (B + E * i));

    // Output
    cout << ans << endl;
}