def di(a,b):
return (a+b+1)//b
c,x,y,z,m,s,f,e,t = map(int,input().split())
if c-x>0:
ans1=di(c+y*di(c-x,z),s)*m
else:
ans1=di(c,s)*m
ans2 = (di((f*(e+1)),s) * m + t)
print(min(ans1, ans2))
ZGVmIGRpKGEsYik6CiAgICByZXR1cm4gKGErYisxKS8vYgoKYyx4LHkseixtLHMsZixlLHQgPSBtYXAoaW50LGlucHV0KCkuc3BsaXQoKSkKaWYgYy14PjA6CiAgICBhbnMxPWRpKGMreSpkaShjLXgseikscykqbQplbHNlOgogICAgYW5zMT1kaShjLHMpKm0KYW5zMiA9IChkaSgoZiooZSsxKSkscykgKiBtICsgdCkKcHJpbnQobWluKGFuczEsIGFuczIpKQ==