N = int(input())
L = list(map(int,input().split()))
K = int(input())
l = 0
r = sum(L)/K
while r-l >10**(-10):
    mid = (l+r)/2
    ans = sum(num//mid for num in L)
    if ans >= K:
        l = mid
    else:
        r = mid
print(l)