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


# 長さ m の棒を K 本作れるか
def can(m: float) -> bool:
    cnt = 0
    for l in L:
        cnt += int(l / m)

    return cnt >= K


lo = 0
hi = max(L)
ans = lo
for _ in range(60):
    m = (lo + hi) / 2
    if can(m):
        ans = max(ans, m)
        lo = m
    else:
        hi = m

print(f'{ans:.10f}')