#include <bits/stdc++.h>
using namespace std;
const int MX = 10000000;
const long long INF = 1000000000000000000;
int main(){
  int T;
  cin >> T;
  int X, A;
  cin >> X >> A;
  int Y, B;
  cin >> Y >> B;
  long long ans = INF;
  for (int i = 0; i <= 10000000; i++){
    long long x = (long long) -B * i;
    long long sum = (long long) Y * i;
    if (x <= T){
      long long D = T - x;
      sum += D / A * X;
      sum += D % A;
      ans = min(ans, sum);
    }
  }
  cout << ans << endl;
}