#include<bits/stdc++.h>
#define double long double
#define int long long
using namespace std;

const double EPS = 1e-8;

template<typename T> struct Vector {
    T x, y;
    Vector(T x = 0, T y = 0): x(x), y(y) {};

    Vector operator+ (const Vector &other) {
        return Vector(x + other.x, y + other.y);
    }
    Vector operator- (const Vector &other) {
        return Vector(x - other.x, y - other.y);
    }
    T operator* (const Vector &other) {
        return x * other.x + y * other.y;
    }
    Vector operator* (const double &other) {
        return Vector(x * other, y * other);
    }
    T operator% (const Vector &other) {
        return x * other.y - y * other.x;
    }
    double abs() {
        return sqrt(x * x + y * y);
    }
    istream & operator>> (istream & in) {
        T x_, y_;
        in >> x_ >> y_;
        x = x_, y = y_;
        return in;
    }
};

template<typename T> struct Point {
    T x, y;
    Point(T x = 0, T y = 0): x(x), y(y) {};

    Point operator+ (const Vector<T> &other) {
        return Point(x + other.x, y + other.y);
    }
    Vector<T> operator- (const Point &B) {
        return Vector<T>(x - B.x, y - B.y);
    }
    bool operator< (const Point &B) {
        return (B.x == x ? y < B.y : x < B.x);
    }
};

template<typename T> bool cw(Vector<T> A, Vector<T> B) {
    return (A % B < -EPS);
}

template<typename T> bool ccw(Vector<T> A, Vector<T> B) {
    return (A % B > EPS);
}

template<typename T> double dist(Point<T> A, Point<T> Q, Point<T> P) {
    if ((A - Q) * (P - Q) < 0) return min((A - P).abs(), (A - Q).abs());
    return abs((A - P) % (Q - P)) / (Q - P).abs();
}

template<typename T> istream & operator>> (istream & in, Point<T> &a) {
    T x_, y_;
    in >> x_ >> y_;
    a.x = x_, a.y = y_;
    return in;
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    freopen("hull.in", "r", stdin);
    freopen("hull.out", "w", stdout);
    vector<Point<int>> lower, upper, all_points;
    int n;
    cin >> n;
    all_points.resize(n);
    for (int i = 0; i < n; i++) cin >> all_points[i];
    sort(all_points.begin(), all_points.end());
    Vector<int> pivot = all_points.back() - all_points.front();
    for (int i = 0; i < n; i++) {
        if (i == 0 || i == n - 1) upper.push_back(all_points[i]), lower.push_back(all_points[i]);
        else if (cw(all_points[i] - all_points.front(), pivot)) upper.push_back(all_points[i]);
        else lower.push_back(all_points[i]);
    }
    vector<Point<int>> uh, lh;
    for (int i = 0; i < upper.size(); i++) {
        while(uh.size() > 1 && !cw(uh.back() - uh[uh.size() - 2], upper[i] - uh.back())) uh.pop_back();
        uh.push_back(upper[i]);
    }
    for (int i = 0; i < lower.size(); i++) {
        while(lh.size() > 1 && !ccw(lh.back() - lh[lh.size() - 2], lower[i] - lh.back())) lh.pop_back();
        lh.push_back(lower[i]);
    }
    cout << lh.size() + uh.size() - 2 << "\n";
    for (auto i : lh) cout << i.x << " " << i.y << "\n";
    for (int i = uh.size() - 2; i >= 1; i--) cout << uh[i].x << " " << uh[i].y << "\n";
}