#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
#define fix(x) fixed << setprecision(x)
#define asc(x) x, vector<x>, greater<x>
#define rep(i, n) for(ll i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll t,x,a,y,b,ans = (1LL<<60);
    cin >> t >> x >> a >> y >> b;
    rep(i,1e7){
        if(t+b*i<0) continue;
        chmin(ans, i*y+(t+b*i)/a*x+(t+b*i)%a);
    }
    cout << ans << '\n';
    return 0;
}