def read_data():
    N = int(input())
    Ls = list(map(int, input().split()))
    K = int(input())
    return N, Ls, K

def solve(N, Ls, K):
    eps = 10**-12
    lower = 1/K - eps
    upper = max(Ls) + eps
    while upper - lower > eps:
        mid = (upper + lower) / 2
        if is_valid(mid, Ls, K):
            lower = mid
        else:
            upper = mid
    return (upper + lower) / 2

def is_valid(mid, Ls, K):
    count = 0
    for L in Ls:
        count += int(L / mid)
    return count >= K

N, Ls, K = read_data()
print(solve(N, Ls, K))