def min(x,y):
    if x>=y:
        return y
    elif y>=x:
        return x


c, x, y, z, m, s,f, e, t= input().split()
c = int(c)
x = int(x)
y = int(y)
z = int(z)
m = int(m)
s = int(s)
f = int(f)
e = int(e)
t = int(t)

time=0
time1=0
time2=0
if c<=x:
    if c%s==0:
        time = m*(c//s)
    else:
        time = (m*(c//s))+m
    print(time)
elif c>x:
    newstoragecost=0
    if (c-x)%z ==0:
        newstoragecost = y*((c-x)//z)
        money = c + newstoragecost
        if money % s == 0:
            time1 = (money // s)* m
        else:
            time1 = ((money // s)* m) + m
    else:
        newstoragecost = (y*((c-x)//z)) + y
        money = c + newstoragecost
        if money % s == 0:
            time1 = (money // s)* m
        else:
            time1 = ((money // s)* m) + m
    infantrycost= (e+1)*f
    if infantrycost % s == 0:
        time2 = (infantrycost // s) * m +t
    else:
        time2 = ((infantrycost// s) * m) + m + t
    print (min(time1, time2))