import sys
input = sys.stdin.readline

N=int(input())
L=list(map(int,input().split()))
K=int(input())

OK=max(L)/K
NG=sum(L)/K

while NG-OK>=10**(-9):
    mid=(OK+NG)/2

    ST=0
    for l in L:
        ST+=l//mid

        if ST>=K:
            break

    if ST>=K:
        OK=mid
    else:
        NG=mid

print(OK)