#include <iostream>
#include <cassert>
#include <vector>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int a, b, c, d, e; cin >> a >> b >> c >> d >> e;
  int ans = a - b;
  for (int i = 1; i <= c; i++) {
    ans = max(ans, (a + d *i) - (b + e * i));
  }
  cout << ans << endl;
  return 0;
}