---

import sys

def main():
    data = sys.stdin.read().split()
    n = int(data[0])
    free = {True: 0, False: 0}  # True — горловина слева, False — справа
    prev_start = 0
    for i in range(1, n + 1):
        t = int(data[i])
        left = t < 0
        start = max(prev_start, free[left])
        free[left] = start + abs(t)
        prev_start = start
    print(max(free[True], free[False]))

main()