#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;
//using P = pair<int, int>;
using namespace std;

const double eps = 1e-10;
#define equals(a, b) (fabs((a)-(b)) < eps)

// 点
struct Point
{
    double x, y;
    Point(double x=0, double y=0): x(x), y(y) {}
    double norm()
    {
        return x*x+y*y;
    }
    double abs()
    {
        return sqrt(norm());
    }

    Point operator+(const Point& p)const
    {
        return Point(x + p.x, y + p.y);
    }
    Point operator-(const Point& p)const
    {
        return Point(x - p.x, y - p.y);
    }
    Point operator*(const double k)const
    {
        return Point(x * k, y * k);
    }
    Point operator/(const double k)const
    {
        return Point(x / k, y / k);
    }
    bool operator<(const Point& p)const
    {
        if (x != p.x)
        {
            return x < p.x;
        }
        return y < p.y;
    }
    bool operator==(const Point& p)const
    {
        return fabs(x - p.x) < eps and fabs(y - p.y) < eps;
    }
};

using Vector = Point;

// 内積
double dot(Vector a, Vector b)
{
    return a.x * b.x + a.y * b.y;
}

// 外積
double cross(Vector a, Vector b)
{
    return a.x * b.y - a.y * b.x;
}
// 線分
struct Segment
{
    Segment(Point a=Point(), Point b=Point()):p1(a), p2(b) {}
    Point p1, p2;
};
using Line = Segment;

// 円
class Circle
{
public:
    Point c;
    double r;
    Circle(Point c = Point(), double r = 0.0): c(c), r(r) {}
};

// 多角形
using Polygon = vector<Point>;


// ベクトルaとbの直行判定
// Verify
bool isOrthogonal(Vector a, Vector b) {
    return equals(dot(a, b), 0.0);
}
bool isOrthogonal(Point a1, Point a2, Point b1, Point b2) {
    return isOrthogonal(a1-a2, b1-b2);
}
bool isOrthogonal(Segment s1, Segment s2) {
    return equals(dot(s1.p2-s1.p1, s2.p2-s2.p1), 0.0);
}

// ベクトルaとbの平行判定
// Verify
bool isParallel(Vector a, Vector b) {
    return equals(cross(a, b), 0.0);
}
bool isParallel(Point a1, Point a2, Point b1, Point b2) {
    return isParallel(a1-a2, b1-b2);
}
bool isParallel(Segment s1, Segment s2) {
    return equals(cross(s1.p2-s1.p1, s2.p2-s2.p1), 0.0);
}

// 射影
// verify
Point project(Segment s, Point p) {
    Vector base = s.p2 - s.p1;
    double r = dot(p - s.p1, base) / base.norm();
    return s.p1 + base * r;
}

// 反射
// verify
Point reflect(Segment s, Point p) {
    return p + (project(s, p) - p) * 2.0;
}

// ２点間の距離
double getDistance(Point a, Point b) {
    return (a-b).abs();
}

// 直線Lと、点Pの距離
// verify
double getDistanceLP(Line l, Point p)
{
    return abs(cross(l.p2 - l.p1, p - l.p1) / Point(l.p2 - l.p1).abs());
}

// 線分sと点pの距離
double getDistanceSP(Segment s, Point p) {
    if (dot(s.p2 - s.p1, p-s.p1) < 0.0) return (p - s.p1).abs();
    if (dot(s.p1 - s.p2, p-s.p2) < 0.0) return (p - s.p2).abs();
    return getDistanceLP((Line)s, p);
}


// 反時計回り
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;

// verify
int ccw(Point p0, Point p1, Point p2) {
    Vector a = p1 - p0;
    Vector b = p2 - p0;
    if (cross(a, b) > eps) return COUNTER_CLOCKWISE;
    if (cross(a, b) < -eps) return CLOCKWISE;
    if (dot(a, b) < -eps) return ONLINE_BACK;
    if (a.norm() < b.norm()) return ONLINE_FRONT;
    return ON_SEGMENT;
}

// 線分の交差判定
// verify
bool intersect(Point p1, Point p2, Point p3, Point p4) {
    return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 and ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0);
}
// verify
bool intersect(Segment s1, Segment s2) {
    return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}

// 線分s1と線分s2の距離
//verify
double getDistance(Segment s1, Segment s2) {
    if (intersect(s1, s2)) return 0.0;
    return min(min(getDistanceSP(s1, s2.p1), getDistanceSP(s1, s2.p2)), min(getDistanceSP(s2, s1.p1), getDistanceSP(s2, s1.p2)));
}

// 線分の交点
// verify
Point getCrossPoint(Segment s1, Segment s2) {
    Vector base = s2.p2 - s2.p1;
    double d1 = abs(cross(base, s1.p1 - s2.p1));
    double d2 = abs(cross(base, s1.p2 - s2.p1));
    double t = d1 / (d1 + d2);
    return s1.p1 + (s1.p2 - s1.p1) * t;
}


// 円cと線分lの交点
//verify
pair<Point, Point> getCrossPoints(Circle c, Line l) {
    //assert(intersect(c, l)); ?
    Vector pr = project(l, c.c);
    Vector e = (l.p2 - l.p1) / (l.p2 - l.p1).abs();
    double base = sqrt(c.r * c.r - (pr - c.c).norm());
    return make_pair(pr + e * base, pr - e * base);
}

// 円と円の交点
double arg(Vector p) { return atan2(p.y, p.x); }
Vector polar(double a, double r) { return Point(cos(r) * a, sin(r) * a); }

// verify
pair<Point, Point> getCrossPoints(Circle c1, Circle c2) {
    // assert(intersect(c1, c2));
    double d = (c1.c - c2.c).abs();
    double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2  * c1.r * d));
    double t = arg(c2.c - c1.c);
    return make_pair(c1.c + polar(c1.r, t + a), c1.c + polar(c1.r, t-a));
}

// 点の内包
// IN 2, ON 1, OUT 0
// verify
int contains(Polygon g, Point p) {
    int n = g.size();
    bool x = false;
    for (int i = 0; i < n; ++i) {
        Point a = g[i] - p, b = g[(i + 1) % n] - p;
        if (abs(cross(a, b)) < eps and dot(a, b) < eps) return 1;
        if (a.y > b.y) swap(a, b);
        if (a.y < eps and eps < b.y and cross(a, b) > eps) x = !x;
    }
    return (x ? 2 : 0);
}

// 凸包
Polygon andrewScan(Polygon s) {
    Polygon u, l;
    if (s.size() < 3) return s;
    sort(s.begin(), s.end());
    u.push_back(s[0]);
    u.push_back(s[1]);
    l.push_back(s[s.size()-1]);
    l.push_back(s[s.size()-2]);

    for (int i = 2; i < s.size(); ++i) {
        for (int n = u.size(); n >= 2 and ccw(u[n-2], u[n-1], s[i]) == COUNTER_CLOCKWISE; --n) {
            u.pop_back();
        }
        u.push_back(s[i]);
    }

    for (int i = s.size()-3; i>=0; --i) {
        for (int n = l.size(); n>=2 and ccw(l[n-2], l[n-1], s[i]) == COUNTER_CLOCKWISE; --n) {
            l.pop_back();
        }
        l.push_back(s[i]);
    }

    reverse(l.begin(), l.end());
    for (int i = u.size() - 2; i >= 1; --i) l.push_back(u[i]);
    return l;
}

// 平面走査
#define BOTTOM 0
#define LEFT 1
#define RIGHT 2
#define TOP 3

class EndPoint {
public:
    Point p;
    int seg, st;
    EndPoint() {}
    EndPoint(Point p, int seg, int st) : p(p), seg(seg), st(st) {}

    bool operator<(const EndPoint &ep) const {
        if (p.y == ep.p.y) {
            return st < ep.st;
        }else return p.y < ep.p.y;
    }
};

EndPoint EP[2 * 100000];

int manhattanIntersection(vector<Segment> S) {
    int n = S.size();

    for (int i = 0, k = 0; i < n; ++i) {
        if (S[i].p1.y == S[i].p2.y) {
            if (S[i].p1.x > S[i].p2.x) swap(S[i].p1, S[i].p2);
        } else if (S[i].p1.y > S[i].p2.y) swap(S[i].p1, S[i].p2);

        if (S[i].p1.y == S[i].p2.y) {
            EP[k++] = EndPoint(S[i].p1, i, LEFT);
            EP[k++] = EndPoint(S[i].p2, i, RIGHT);
        }
        else {
            EP[k++] = EndPoint(S[i].p1, i, BOTTOM);
            EP[k++] = EndPoint(S[i].p2, i, TOP);
        }
    }

    sort(EP, EP + (2 * n));

    set<int> BT;
    BT.insert(100000001); // 番兵
    int cnt = 0;

    for (int i = 0; i < 2 * n; ++i) {
        if (EP[i].st == TOP) {
            BT.erase(EP[i].p.x);
        }
        else if (EP[i].st == BOTTOM) {
            BT.insert(EP[i].p.x);
        }
        else if (EP[i].st == LEFT) {
            auto b = lower_bound(BT.begin(), BT.end(), S[EP[i].seg].p1.x);
            auto e = upper_bound(BT.begin(), BT.end(), S[EP[i].seg].p2.x);
            cnt += distance(b, e);
        }
    }

    return cnt;

}

int main() {
    int n;
    cin >> n;
    Polygon g;

    rep(i, n) {
        int x, y;
        cin >> x >> y;
        Point a(x, y);
        g.push_back(a);
    }

    Polygon ret = andrewScan(g);
    cout << ret.size() << endl;

    int p = 0;
    double a= 1e9, b = 1e9;
    rep(i, ret.size()) {
        if (ret[i].y < b) {
            a = ret[i].x;
            b = ret[i].y;
            p = i;
        }
        else if (ret[i].y == b and ret[i].x < a) {
            a = ret[i].x;
            p = i;
        }
    }

    rep(i, ret.size()) {
        cout << ret[(p+i)%ret.size()].x << " " << ret[(p+i)%ret.size()].y << endl;
    }
}



Measured memory_bytes: 14092