from bisect import*
n=int(input())
s=input()
m=-n
p=1
a=[]
for c in s:
  if c=='+':
    a+=p,
    p+=1
  if c=='-':
    a+=m,
    m+=1
  if c=='0':
    a+=0,
l=[]
for i in range(n):
  j=bisect_left(l,a[i])
  if j<len(l):
    l[j]=a[i]
  else:
    l+=a[i],
print(len(l))