N = int(input())
X = 10 ** 10
L = [l*X for l in list(map(int,input().split()))]
K = int(input())
lb = 0
ub = 10 ** 20

def check(x):
    tmp = 0
    for l in L:
        tmp += l//x
    return tmp >= K

while ub - lb > 1:
    mid = (ub + lb) // 2
    if check(mid):
        lb = mid
    else:
        ub = mid
print(lb/X)