from math import ceil
c,x,y,z,m,s,f,e,t = map(int, input().split())
fight  = ceil((e+1)*f/s)*m + t
if c>x:
    earn = ceil((ceil((c-x)/z)*y + c)/s)*m
else:
    earn = ceil(c/s)*m
print(min(int(fight),int(earn)))