signed main() {
    ios::sync_with_stdio(0), cin.tie(0);
    int n; cin >> n;
    vector<vector<int>> g(2001);
    vector<pair<int, int>> a(n);
    for (int i = 0; i < n; i++) {
        int u, v;
        cin >> u >> v;
        a[i].first = u + 1000;
        a[i].second = v + 1000;
        g[u + 1000].push_back(v + 1000);
        g[v + 1000].push_back(u + 1000);
    }
    int ans = 0;
    for (int i = 0; i < n; i++) {
        int x = a[i].first;
        int y = a[i].second;
        bool l = 0, r = 0, u = 0, d = 0;
        for (auto k : g[y]) {
            if (k > x) {
                r = 1;
            } else if (k < x) {
                l = 1;
            }       
        }
        for (auto k : g[x]) {
            if (k > y) {
                u = 1;
            } else if (k < y) {
                d = 1;
            }
        }
        if (l == 1 and r == 1 and u == 1 and d == 1) {
            ans += 1;
        }
    }
    std::cout << ans << "\n";
    return 0;
}

void solve() {
    int n, x, q;
    cin >> n >> x >> q;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        a[i] -= i;
    }
    map<int, int> f;
    for (int i = 0; i < x; i++) {
        f[a[i]]++;
    }
    multiset<int, greater<int>> mt;
    for (auto it : f) {
        mt.insert(it.second);
    }
    vector<int> ans(n - x + 1);
    ans[0] = x - *mt.begin();
    for (int i = x; i < n; i++) {
        int cur = i;
        int beg = i - x;
        mt.erase(mt.find(f[a[beg]]));
        f[a[beg]]--;
        mt.insert(f[a[beg]]);
        mt.erase(mt.find(f[a[cur]]));
        f[a[cur]]++;
        mt.insert(f[a[cur]]);
        ans[beg] = x - *mt.begin();
    }
    while (q--) {
        int l, r;
        cin >> l >> r;
        cout << ans[l - 1] << "\n";
    }
}

    multiset<int, greater<int>> mt;
    for(int i = 1; i <= n; i++) {
        mt.insert(0);
    }