#include <iostream>
using namespace std;
int main()
{
    int a, b, c, d, e;
    cin >> a >> b >> c >> d >> e;
    int mx = INT32_MIN;
    for (int i = 0; i <= c; i++)
    {
        mx = max(mx, a + i * d - b - e * i);
    }
    cout << mx << endl;
}