from bisect import bisect_left
import sys, math
sys.setrecursionlimit(10**8)
sys.set_int_max_str_digits(0)

N = int(input())
S = list(input())

num = 1
for i in range(N):
    if S[i] == '+':
        S[i] = num
        num += 1
    elif S[i] == '0':
        S[i] = 0
num = -1
for i in range(N - 1, -1, -1):
    if S[i] == '-':
        S[i] = num
        num -= 1
L = []
for s in S:
    idx = bisect_left(L, s)
    if len(L) == idx:
        L.append(s)
    else:
        L[idx] = s

print(len(L))