import sys

input = sys.stdin.readline


def get_num_tree(length):
    ans = sum(int(tree / length) for tree in L)
    return ans


n = int(input())
L = tuple(map(int, input().split()))
k = int(input())

l = 0
r = max(L) + 1
# while r - l >= 10 ** (-9):
#     mid = (l + r) / 2
#     if get_num_tree(mid) >= k:
#         l = mid
#     else:
#         r = mid
for _ in range(100):
    mid = (l + r) / 2
    if get_num_tree(mid) >= k:
        l = mid
    else:
        r = mid

print(l)