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

def solve(N, Ls, K):
    if K == 1:
        return max(Ls)
    eps = 5*10**-10
    sumLs = sum(Ls)
    maxLs = max(Ls)
    lower = max(maxLs/K, sumLs/(K + N)) - eps
#    lower = maxLs/K - eps
    upper = min(sumLs/K, maxLs) + eps
    while upper - lower > eps and (upper - lower)/lower > eps:
        mid = (upper + lower) / 2
        if sum(int(L/mid) for L in Ls) >= K:
            lower = mid
        else:
            upper = mid
    return (lower + upper)/2


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