1

var
  n, a, b, x, y, z, f, e, m, s, t, c: real;

  SpM: real;

begin
  read(c ,x, y, z, m, s, f, e, t);

  a := ceil((e + 1) * f / s) * m + t;


  n := ceil((c - x) / z);

 if n<0 then n:= 0;

  b := ceil((c + n*y) / s) * m;

  println(min(a, b));

end.