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

hoho = 0
hehe = 0
hihi = 0
if c <= x:
    if c % s == 0:
        hoho = m * (c // s)
    else:
        hoho = (m * (c // s)) + m
    print(hoho)
elif c > x:
    haha = 0
    if (c - x) % z == 0:
        haha = y * ((c - x) // z)
        huhu = c + haha
        if huhu % s == 0:
            hehe = (huhu // s) * m
        else:
            hehe = ((huhu // s) * m) + m
    else:
        haha = (y * ((c - x) // z)) + y
        huhu = c + haha
        if huhu % s == 0:
            hehe = (huhu // s) * m
        else:
            hehe = ((huhu // s) * m) + m
    hyhy = (e + 1) * f
    if hyhy % s == 0:
        hihi = (hyhy // s) * m + t
    else:
        hihi = ((hyhy // s) * m) + m + t
    print(min(hehe, hihi))