#include <iostream>

using namespace std;
int timeCalc(int SumCost, int m, int s)
{
 int res = (SumCost / s) * m;
 if (SumCost % s != 0) res += m;
 return res;
}
int main()
{
 int c, x, y, z, m, s, f, e, t;
 cin » c » x » y » z » m » s » f » e » t;
 int p = e + 1;
 int res = 0;
 int sc = 0;
  if (c > x) {
  int Nh = (c - x) / z;
  if ((c - x) % z != 0) Nh++;
  sc = Nh*y + c;
 }
 else {
  sc = c;
 }
 int sf = p * f;
 int rc = timeCalc(sc, m, s);
 int rf = timeCalc(sf, m, s) + t;
 if (rc > rf) res = rf;
 else res = rc;
 cout « res;
}