#include "testlib.h"
#include <bits/stdc++.h>

using namespace std;

int main(){
  registerValidation();
  long long t=inf.readLong(-10000000ll,10000000ll);inf.readEoln();
  long long x=inf.readLong(1ll,10000000ll);inf.readSpace();
  long long a=inf.readLong(x+1,10000000ll);inf.readEoln();
  long long y=inf.readLong(1ll,10000000ll);inf.readSpace();
  long long b=inf.readLong(1ll,10000000ll);inf.readEoln();
  inf.readEof();

  long long res=8e18;
  for(long long past=0;past<=1e8;past++){
    long long fut=t+past*b;
    if(fut<0){continue;}
    res=min(res,past*y + (fut/a)*x + (fut%a));
  }
  cout << res << "\n";
  return 0;
}