n = int(input())
ls = list(map(int, input().split()))
k = int(input())

low = 0
high = max(ls)
eps = 10**-9

while (high - low) > eps * 2:
    mid = (low + high) / 2
    if (high - low) / mid <= eps * 2:
        break
    
    ct = 0
    for l in ls:
        ct += l // mid
        
    if ct >= k:
        low = mid
    else:
        high = mid

print('{:.20f}'.format(mid))