---

n = int(input())
left_free = 0
right_free = 0
last_start = 0

for _ in range(n):
    t = int(input())
    duration = abs(t)
    if t < 0:
        start = max(last_start, left_free)
        left_free = start + duration
    else:
        start = max(last_start, right_free)
        right_free = start + duration
    last_start = start

RefuelingDuration = max(left_free, right_free)
print(RefuelingDurat