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

def is_ok(arg):
    cnt = 0
    d = (arg*(10**(-9)))
    for i in range(N):
        cnt += lsL[i]//d
    return cnt >= K
 
def meguru_bisect(ng, ok):
    while (abs(ok - ng) > 1):
        mid = (ok + ng) // 2
        if is_ok(mid):
            ok = mid
        else:
            ng = mid
    return ok
print(meguru_bisect(10**20,0)*(10**(-9)))