---

import sys

input_data = list(map(int, sys.stdin.read().split()))
if input_data:
    tasks = input_data[1:]
    processors = [0, 0]
    current_time = 0

    for task in tasks:
        is_negative = int(task < 0)
        current_time = max(current_time, processors[is_negative])
        processors[is_negative] = current_time + abs(task)

    print(max(processors))