#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
using ll = long long;

int main(){
    int t; cin >> t;
    int x, a; cin >> x >> a;
    int y, b; cin >> y >> b;

    ll ans = 1LL << 60;
    for(int i = 0; i < 10000010; i++){
        ll res = 0;
        ll t1 = t;
        res += 1LL*y*i;
        t1 += 1LL*b*i;
        if(t1 < 0) continue;
        ll c1 = t1/a;
        res += x*c1;
        res += t1-a*c1;
        ans = min(ans, res);
    }
    cout << ans << endl;
    return 0;
}