/*
*/

#include <bits/stdc++.h>
using namespace std;
#define ALL(x) (x).begin(), (x).end()
#define REP(i, n) for(ll i=0; i<(ll)(n); i++)
#define RREP(i, n) for(ll i=(ll)(n)-1; i>=0; i--)

template<typename T> int LB(const vector<T>& v, T x) { return lower_bound(ALL(v),x)-v.begin(); }
template<typename T> int UQ(T& v) { sort(ALL(v)); v.erase(unique(ALL(v)),v.end()); return v.size(); }
template<typename T> bool chmax(T& a, T b) { return a<b ? a=b, true : false; }
template<typename T> bool chmin(T& a, T b) { return a>b ? a=b, true : false; }
template<typename T> using rpriority_queue=priority_queue<T,vector<T>,greater<T>>;
using ll=long long; const int INF=1e9+10; const ll INFL=4e18;
using ld=long double; using lll=__int128_t; using ull=unsigned long long;
using VI=vector<int>; using VVI=vector<VI>; using VL=vector<ll>; using VVL=vector<VL>;
using PL=pair<ll,ll>; using VP=vector<PL>; using WG=vector<vector<pair<int,ll>>>;


#ifdef LOCAL
#include "./debug.hpp"
#else
#define debug(...)
#define print_line
#endif



/// @brief LIS
/// @brief 配列 v の最長増加部分列の長さを返す
/// @param strict `true` のとき狭義単調増加
/// @note O(N log(N))
int LisLength(vector<int>& v, bool strict=true) {
    int n=v.size();
    vector<int> dp(n,INF);
    for(int i=0; i<n; i++) {
        auto itr=(strict ? lower_bound(dp.begin(),dp.end(),v[i]) : upper_bound(dp.begin(),dp.end(),v[i]));
        *itr=v[i];
    }
    return find(dp.begin(),dp.end(),INF)-dp.begin();
}

//----------------------------------------------------------

void solve() {
    ll N; cin>>N;
    string S; cin>>S;

    VI A(N);
    int minus=-INF, plus=1;
    REP(i,N) {
        if(S[i]=='+') A[i]=plus++;
        else if(S[i]=='0') A[i]=0;
        else A[i]=minus++;
    }

    cout<<LisLength(A)<<endl;
}

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    //cout<<fixed<<setprecision(15);
    int T=1;
    //cin>>T;
    while(T--) solve();
}