import math

c, x, y, z, m, s, f, e, t = [int(i) for i in input().split()]

if c <= x:
    time_kop = m*math.ceil(c/s)
else:
    kol_hr = math.ceil((c - x) / z)
    ost = s * math.ceil(kol_hr * y / s) - kol_hr * y
    t_hr = (math.ceil(kol_hr * y / s)) * m
    time_kop = t_hr + math.ceil((c - ost) / s) * m

tr = 0
cred_ost = 0
k = math.floor(((e+1)*f)/s)+1
t_tr = t + m*k
if time_kop < t_tr:
    print(time_kop)
else:
    print(t_tr)