#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

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++) {
    ans = max(ans, a - b + d * i - e * i);
  }
  cout << ans << endl;
  return 0;
}