eps = 1e-10
N = int(input())
A = list(map(lambda x: float(x) + eps, input().split()))
K = int(input())


def OK(L):
    cnt = 0
    for a in A:
        cnt += int(a / L)
    return cnt >= K


wa = eps
ac = 1e20
while ac - wa > ac * eps:
    wj = (ac + wa) * 0.5
    if OK(wj):
        wa = wj
    else:
        ac = wj

print("{:.20f}".format((ac + wa) * 0.5))