import numpy as np

N = int(input())
L = np.array(tuple(map(int, input().split())))
K = int(input())
l, r = 0, 10 ** 9

while r - l > 10 ** -9:
    m = (l + r) / 2
    if (L // m).astype(int).sum() < K:
        r = m
    else:
        l = m
print(l)