from bisect import bisect
N = int(raw_input())
L = map(int,raw_input().split())
K = int(raw_input())
ans = 10**4
d,u = 0,10**9
for loop in xrange(100):
    cnt = 0
    for l in L:
        cnt += int(l/ans)
    if cnt < K:
        u = ans
    else:
        d = ans
    ans = (u+d)/2.
print "%.10f"%ans