#line 1 "test/geometry/convex_hull.test.cpp"
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_4_A"
#define ERROR 1e-6

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

#line 1 "test/geometry/../../library/geometry/geometry.cpp"
const double eps = 1e-10;
inline bool eq(double a, double b) { return fabs(a - b) < eps; }
const double pi = acos(-1);

struct Point {
    double x, y;
    Point() {}
    Point(double x, double y) : x(x), y(y) {}
    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*(double k) const { return Point(x * k, y * k); }
    Point operator/(double k) const { return Point(x / k, y / k); }
};
istream &operator>>(istream &is, Point &p) {
    is >> p.x >> p.y;
    return is;
}
ostream &operator<<(ostream &os, Point p) {
    os << fixed << setprecision(10) << p.x << " " << p.y;
    return os;
}
bool sort_x(Point a, Point b) { return a.x != b.x ? a.x < b.x : a.y < b.y; }
bool sort_y(Point a, Point b) { return a.y != b.y ? a.y < b.y : a.x < b.x; }
bool sort_t(Point a, Point b) { return atan2(a.y, a.x) < atan2(b.y, a.y); }
Point rotate(double theta, const Point &p) {
    return Point(cos(theta) * p.x - sin(theta) * p.y, sin(theta) * p.x + cos(theta) * p.y);
}
double radian_to_degree(double r) { return (r * 180.0 / pi); }
double degree_to_radian(double d) { return (d * pi / 180.0); }

struct Line {
    Point a, b;
    Line() {}
    Line(Point a, Point b) : a(a), b(b) {}
    Line(double A, double B, double C) { // Ax + By = C
        if (eq(A, 0))
            a = Point(0, C / B), b = Point(1, C / B);
        else if (eq(B, 0))
            a = Point(C / A, 0), b = Point(C / A, 1);
        else
            a = Point(0, C / B), b = Point(C / A, 0);
    }
    Point vec() const { return b - a; }
};
struct Segment : Line {
    Segment() {}
    Segment(Point a, Point b) : Line(a, b) {}
};

struct Circle {
    Point p;
    double r;
    Circle() {}
    Circle(Point p, double r) : p(p), r(r) {}
};
double norm(const Point &a) { return a.x * a.x + a.y * a.y; }
double abs(const Point &a) { return sqrt(norm(a)); }
double cross(const Point &a, const Point &b) { return a.x * b.y - a.y * b.x; }
double dot(const Point &a, const Point &b) { return a.x * b.x + a.y * b.y; }

Point project(Line l, Point p) {
    double t = dot(p - l.a, l.a - l.b) / norm(l.a - l.b);
    return l.a + (l.a - l.b) * t;
}
Point reflect(Line l, Point p) { return p + (project(l, p) - p) * 2; }
bool parallel(Line a, Line b) { return eq(cross(a.vec(), b.vec()), 0.0); }
bool orthogonal(Line a, Line b) { return eq(dot(a.vec(), b.vec()), 0.0); }
int ccw(const Point &a, Point b, Point c) {
    b = b - a, c = c - a;
    if (cross(b, c) > eps)
        return +1; // "COUNTER_CLOCKWISE"
    if (cross(b, c) < -eps)
        return -1; // "CLOCKWISE"
    if (dot(b, c) < 0)
        return +2; // "ONLINE_BACK"
    if (norm(b) < norm(c))
        return -2; // "ONLINE_FRONT"
    return 0;      // "ON_SEGMENT"
}
bool intersect(const Line &l, const Point &p) { return abs(ccw(l.a, l.b, p)) != 1; }
bool intersect(const Line &l, const Line &m) { return !parallel(l, m) || abs(cross(l.vec(), m.b - l.a)) < eps; }
bool intersect(const Segment &s, const Point &p) { return ccw(s.a, s.b, p) == 0; }
bool intersect(const Line &l, const Segment &s) { return cross(l.vec(), s.a - l.a) * cross(l.vec(), s.b - l.a) < eps; }
double distance(const Line &l, const Point &p);
bool intersect(const Circle &c, const Line &l) { return distance(l, c.p) <= c.r + eps; }
bool intersect(const Circle &c, const Point &p) { return abs(abs(p - c.p) - c.r) < eps; }
bool intersect(const Segment &s, const Segment &t) {
    return ccw(s.a, s.b, t.a) * ccw(s.a, s.b, t.b) <= 0 && ccw(t.a, t.b, s.a) * ccw(t.a, t.b, s.b) <= 0;
}
int intersect(const Circle &c, const Segment &l) {
    if (norm(project(l, c.p) - c.p) - c.r * c.r > eps)
        return 0;
    auto d1 = abs(c.p - l.a), d2 = abs(c.p - l.b);
    if (d1 < c.r + eps && d2 < c.r + eps)
        return 0;
    if ((d1 < c.r - eps && d2 > c.r + eps) || (d1 > c.r + eps && d2 < c.r - eps))
        return 1;
    const Point h = project(l, c.p);
    if (dot(l.a - h, l.b - h) < 0)
        return 2;
    return 0;
}
int intersect(Circle c1, Circle c2) {
    if (c1.r < c2.r)
        swap(c1, c2);
    double d = abs(c1.p - c2.p);
    if (c1.r + c2.r < d)
        return 4; // do not cross
    if (eq(c1.r + c2.r, d))
        return 3; // circumscribed
    if (c1.r - c2.r < d)
        return 2; // intersect
    if (eq(c1.r - c2.r, d))
        return 1; // inscribed
    return 0;     // one circle includes another
}

double distance(const Point &a, const Point &b) { return abs(a - b); }
double distance(const Line &l, const Point &p) { return abs(p - project(l, p)); }
double distance(const Line &l, const Line &m) { return intersect(l, m) ? 0 : distance(l, m.a); }
double distance(const Segment &s, const Point &p) {
    Point r = project(s, p);
    if (intersect(s, r))
        return abs(r - p);
    return min(abs(s.a - p), abs(s.b - p));
}
double distance(const Segment &a, const Segment &b) {
    if (intersect(a, b))
        return 0;
    return min({distance(a, b.a), distance(a, b.b), distance(b, a.a), distance(b, a.b)});
}
double distance(const Line &l, const Segment &s) {
    if (intersect(l, s))
        return 0;
    return min(distance(l, s.a), distance(l, s.b));
}
Point crosspoint(const Line &l, const Line &m) {
    double A = cross(l.vec(), m.vec());
    double B = cross(l.vec(), l.b - m.a);
    if (eq(abs(A), 0.0) && eq(abs(B), 0.0))
        return m.a;
    return m.a + (m.b - m.a) * B / A;
}
Point crosspoint(const Segment &l, const Segment &m) { return crosspoint(Line(l), Line(m)); }
pair<Point, Point> crosspoint(const Circle &c, const Line l) {
    Point pr = project(l, c.p);
    Point e  = (l.b - l.a) / abs(l.b - l.a);
    if (eq(distance(l, c.p), c.r))
        return {pr, pr};
    double base = sqrt(c.r * c.r - norm(pr - c.p));
    return {pr - e * base, pr + e * base};
}
pair<Point, Point> crosspoint(const Circle &c, const Segment &l) {
    Line aa = Line(l.a, l.b);
    if (intersect(c, l) == 2)
        return crosspoint(c, aa);
    auto ret = crosspoint(c, aa);
    if (dot(l.a - ret.first, l.b - ret.first) < 0)
        ret.second = ret.first;
    else
        ret.first = ret.second;
    return ret;
}
pair<Point, Point> crosspoint(const Circle &c1, const Circle &c2) {
    double d = abs(c1.p - c2.p);
    double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
    double t = atan2(c2.p.y - c1.p.y, c2.p.x - c1.p.x);
    Point p1 = c1.p + Point(cos(t + a) * c1.r, sin(t + a) * c1.r);
    Point p2 = c1.p + Point(cos(t - a) * c1.r, sin(t - a) * c1.r);
    return {p1, p2};
}
vector<Point> convex_hull(vector<Point> &p) {
    int n = (int)p.size(), k = 0;
    if (n <= 2)
        return p;
    sort(p.begin(), p.end(), sort_x);
    vector<Point> ch(2 * n);
    for (int i = 0; i < n; ch[k++] = p[i++]) {
        while (k >= 2 && cross(ch[k - 1] - ch[k - 2], p[i] - ch[k - 1]) < -eps)
            --k;
    }
    for (int i = n - 2, t = k + 1; i >= 0; ch[k++] = p[i--]) {
        while (k >= t && cross(ch[k - 1] - ch[k - 2], p[i] - ch[k - 1]) < -eps)
            --k;
    }
    ch.resize(k - 1);
    return ch;
}
#line 9 "test/geometry/convex_hull.test.cpp"

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    vector<Point> x(n);
    for (int i = 0; i < n; ++i) {
        cin >> x[i];
    }
    auto ret = convex_hull(x);
    cout << ret.size() << "\n";
    int idx = 0;
    for (int i = 1; i < (int)ret.size(); ++i) {
        if (ret[idx].y > ret[i].y || (eq(ret[idx].y, ret[i].y) && ret[idx].x > ret[idx].x))
            idx = i;
    }
    for (int i = 0; i < (int)ret.size(); ++i) {
        cout << int(ret[(idx + i) % int(ret.size())].x) << " " << int(ret[(idx + i) % int(ret.size())].y) << "\n";
    }
    return 0;
}



Measured memory_bytes: 5440