import math
c,x,y,z,m,s,f,e,t = map(int, input().split())
a = math.ceil((e + 1) * f / s) * m + t
if c>x:
       n = math.ceil((c - x) / z)
else:
       n = 0
b = math.ceil((c+n*y)/s)*m
print(min(a,b))