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

int main() {
    long long T, X, A, Y, B;
    cin >> T >> X >> A >> Y >> B;
    long long ans = (T/A)*X + T%A;
    long long now = T - T%A;
    for(int i = 0; i < 2*(1e7); ++i) {
        now += A;
        long long wait = T - (now - ((now-T-1)/B+1)*B);
        ans = min(ans, (now/A)*X + (now-(T-wait))/B*Y + wait);
    }
    cout << ans << endl;
}