#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001

int main(){
	
	
	int n;
	cin>>n;
	string s;
	cin>>s;
	
	vector dp(50,vector<int>(2,-Inf32));
	dp[0][0] = 0;
	
	rep(i,n){
		vector ndp(50,vector<int>(2,-Inf32));
		rep(j,50){
			rep(k,2){
				if(dp[j][k]==-Inf32)continue;
				rep(l,2){
					int nv = dp[j][k];
					int nj = j;
					if(k==0&&l==1)nj++;
					if(nj>=50)continue;
					
					if(s[i]=='?')nv++;
					else{
						if(s[i]=='+'){
							if(l==0)nv++;
							else nv--;
						}
						else{
							if(l==0)nv--;
							else nv++;
						}
					}
					if(nv<0)continue;
					//cout<<i<<','<<nj<<','<<nv<<endl;
					ndp[nj][l] = max(ndp[nj][l],nv);
				
					
				}
					
			}
		}
		swap(dp,ndp);
	}
	
	rep(i,50){
		rep(j,2){
			if(dp[i][j]!=-Inf32){
				cout<<i<<endl;
				return 0;
			}
		}
	}
	
	return 0;
}