def max_sub(arr):
    max_val = 0
    summ = 0
    for i in range(len(arr)):
        summ += arr[i]
        if i == 0:
            max_val = summ
        elif summ < arr[i]:
            summ = arr[i]
            if arr[i] > max_val:
                max_val = arr[i]
        elif summ > max_val:
            max_val = summ

    return max_val


arr = [-2, 1, -3, 4, -1, 2, 1, -5, 4]
# print(max_sub(arr))