#include <bits/stdc++.h>
using namespace std;

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
#define SZ(v) ((int)(v).size())

using lint = long long;
using ld = long double;

const int INF = 2000000000;
const lint LINF = 1000000000000000000;
// 真上から反時計回り
const int di[] = {-1, 0, 1, 0};
const int dj[] = {0, -1, 0, 1};
const int di8[] = {-1, -1, 0, 1, 1, 1, 0, -1};
const int dj8[] = {0, -1, -1, -1, 0, 1, 1, 1};

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false); cin.tie(nullptr);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(15);
    }
} setupio;

template <class T>
bool chmin(T &a, const T &b) {
    return a > b ? a = b, 1 : 0;
}
template <class T>
bool chmax(T &a, const T &b) {
    return a < b ? a = b, 1 : 0; 
}
template <class T>
T mypow(T a, T b) {
    T res = 1;
    while (b) {
        if (b & 1) { res *= a; }
        a *= a; b >>= 1;
    }
    return res;
}
template <class T>
T modpow(T a, T b, T mod) {
    T res = 1;
    while (b) {
        if (b & 1) { res = (res * a) % mod; }
        a = (a * a) % mod; b >>= 1;
    }
    return res;
}

vector<int> LIS(const vector<int> &a) {
    int n = a.size();
    vector<int> dp(n + 1, INT_MAX), prev(n);
    dp[0] = INT_MIN;
    for (int i = 0; i < n; i++) {
        int len = lower_bound(dp.begin(), dp.end(), a[i]) - dp.begin();
        prev[i] = dp[len - 1];
        dp[len] = min(dp[len], a[i]);
    }
    
    vector<int> lis;
    int cur;
    for (int i = n; i >= 0; i--) {
        if (dp[i] != INT_MAX) {
            cur = dp[i];
            break;
        }
    }
    int i = n - 1;
    while (cur != INT_MIN) {
        if (a[i] == cur) {
            lis.emplace_back(cur);
            cur = prev[i];
        }
        i--;
    }
    reverse(lis.begin(), lis.end());
    return lis;
}


int main() {
    int N;
    string S;
    cin >> N >> S;
    int posi = 1, nega = -INF;
    vector<int> A(N);
    rep(i, N) {
        if (S[i] == '-') {
            A[i] = nega; nega++;
        } else if (S[i] == '0') {
            A[i] = 0;
        } else {
            A[i] = posi; posi++;
        }
    }
    cout << SZ(LIS(A)) << "\n";
}