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

#ifdef _RUTHEN
#include <debug.hpp>
#else
#define show(...) true
#endif

using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
template <class T> using V = vector<T>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll T, X, A, Y, B;
    cin >> T >> X >> A >> Y >> B;
    ll ans = 1LL << 60;
    for (int i = 0; i <= 100000000; i++) {
        ll cur = X * i, curd = A * i;
        if (curd <= T) {
            ans = min(ans, cur + T - curd);
        } else {
            // curd > T
            ll d = curd - T;
            ll q = (d + B - 1) / B;
            ll r = q * B - d;
            ans = min(ans, cur + q * Y + r);
        }
    }
    cout << ans << '\n';
    return 0;
}