#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

// calc ceil(a/b) 
template<typename T>
T ceil_div(T a, T b){
    return (a+b-1)/b;
}

const ll inf = 1e18;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    ll t, x, a, y, b; cin >> t >> x >> a >> y >> b;
    ll ans = inf;
    for(ll p = 0; p < b; p++){
        ll tt = p*a;
        ll tmp = p*x;
        if(tt >= t){
            ll dist = tt-t;
            ll c = ceil_div(dist, b);
            tmp += c*y + (c*b-dist);
        }else{
            tmp += t-tt;
        }
        chmin(ans, tmp);
    }

    for(ll q = 0; q < a; q++){
        ll tt = -q*b;
        ll tmp = q*y;
        if(tt <= t){
            ll dist = t-tt;
            ll c = dist/a;
            tmp += c*x + (dist-c*a);
        }else{
            continue;
        }
        chmin(ans, tmp);
    }
    cout << ans << endl;
}