def f(lst):
    a = lst[0]
    b = lst[1]
    c = lst[2]
    d = lst[3]
    e = lst[4]
    f = lst[5]
    g = lst[6]
    h = lst[7] + 1
    i = lst[8]

    gold_to_get_all_footmans = g * h
    time_footmans = (
                        gold_to_get_all_footmans // f
                        if gold_to_get_all_footmans % f == 0
                        else gold_to_get_all_footmans // f + 1) * e + i

    _ = a - b if a - b > 0 else 0
    credits_to_build_all = (
                               _ // d
                               if _ % d == 0
                               else _ // d + 1) * c

    times_to_get_credits_for_buildings = (
        c // f
        if c % f == 0
        else (c // f) + 1
    )

    a -= times_to_get_credits_for_buildings * f - credits_to_build_all
    time_credits = times_to_get_credits_for_buildings * e \
                   + (a // f
                      if a % f == 0
                      else (a // f) + 1) * e

    return time_footmans, time_credits


lst = list(map(int, input().split()))
print(min(f(lst)))