def max_sequence(arr):
    m = 0
    s = 0
    for i in range(len(arr)):
        k = 0
        ar = arr[s:]
        for i in ar:
            k+=i
            if k > m:
                m = k
        s+=1
        
    print(m)

max_sequence([-2, 1, -3, 4, -1, 2, 1, -5, 4])

def maxSequence(lst):
    if not lst:
        return 0
    maxsum = max(map(sum, [sub[:x] for sub in [lst[i:] for i in range(len(lst))] for x in range(1-len(sub), 0)]))
    return maxsum if maxsum>0 else 0

assert maxSequence([-2, 1, -3, 4, -1, 2, 1, -5, 4]) == 6
assert maxSequence([-2, -3, 0]) == 0
assert maxSequence([]) == 0