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

OK=10**(-11)
NG=10**11

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

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

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

print(OK)