import sys
import math
import bisect
from heapq import heapify, heappop, heappush
from collections import deque, defaultdict, Counter
from functools import lru_cache
from itertools import accumulate, combinations, permutations, product

sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
MOD99 = 998244353

input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()
SMI = lambda: input().split()
SLI = lambda: list(SMI())
EI = lambda m: [NLI() for _ in range(m)]


def main():
    N = NI()
    L = NLI()
    K = NI()
    def judge(X):
        res = 0
        for l in L:
            res += l * 10**9 // X
        return res >= K

    ok = 0
    ng = 10**18+1
    while abs(ng-ok) > 1:
        X = (ok + ng) // 2
        if judge(X):
            ok = X
        else:
            ng = X

    print(ok / 10**9)


if __name__ == "__main__":
    main()