#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

int main() {
  ll T;
  cin >> T;

  ll X, A;
  cin >> X >> A;

  ll Y, B;
  cin >> Y >> B;
  ll min_cost = LLONG_MAX;

  if (T > 0) {
    ll d = T / A;

    for (ll i = 0; i <= 10000000; ++i) {
      ll step_cnt = d + i;
      ll al = step_cnt * A;
      ll cost = X * step_cnt;

      if (T < al) {
        ll over_len = al - T;
        ll back_cnt = (over_len + B - 1) / B;
        al -= back_cnt * B;
        cost += Y * back_cnt;
      }

      ll remain = T - al;
      cost += remain;

      min_cost = min(min_cost, cost);
    }
  } else {
    for (ll i = 0; i <= 10000000; ++i) {
      ll step_cnt = i;
      ll al = step_cnt * A;
      ll cost = X * step_cnt;
      ll back_cnt = 0;

      if (T < al) {
        ll over_len = al - T;
        back_cnt = (over_len + B - 1) / B;
        al -= back_cnt * B;
        cost += Y * back_cnt;
      }

      ll remain = T - al;
      cost += remain;

      min_cost = min(min_cost, cost);
    }
  }

  cout << min_cost << endl;

  return 0;
}