#include <bits/stdc++.h>
using namespace std;
#define int long long
#define stoi stoll
using ll=long long;
using vi=vector<int>;
using pii=pair<int,int>;
#define ALL(c) begin(c),end(c)
#define RALL(c) rbegin(c),rend(c)
#define ITR(i,b,e) for(auto i=(b);i!=(e);++i)
#define FORE(x,c) for(auto &x:c)
#define REPF(i,a,n) for(int i=a,i##len=(int)(n);i<i##len;++i)
#define REP(i,n) REPF(i,0,n)
#define REPR(i,n) for(int i=(int)(n);i>=0;--i)
#define SZ(c) ((int)c.size())
#define CONTAIN(c,x) (c.find(x)!=end(c))
#define INSEG(l,x,r) ((l)<=(x)&&(x)<(r))
#define dump(...)
#define pb push_back
#define _ 0
const signed INF_=1001001001; const long long INF=1001001001001001001LL;
const int DX[9]={0,1,0,-1,1,1,-1,-1,0},DY[9]={-1,0,1,0,-1,1,1,-1,0};
template<class T> ostream& operator<<(ostream &os,const vector<T> &v) {
    ITR(i,begin(v),end(v))os<<*i<<(i==end(v)-1?"":" ");return os;}
template<class T> istream& operator>>(istream &is,vector<T> &v) {
    ITR(i,begin(v),end(v)) is>>*i;return is;}
template<class T,class U> istream& operator>>(istream &is, pair<T,U> &p) {
    is>>p.first>>p.second;return is;}
template<class T, class U> bool chmax(T &a,const U &b){return a<b?a=b,1:0;}
template<class T, class U> bool chmin(T &a,const U &b){return a>b?a=b,1:0;}
template <class T> void PSUM(T& c) {partial_sum(begin(c), end(c), begin(c));}
template<class T> using heap=priority_queue<T,vector<T>,greater<T>>;
struct before_main_function {
    before_main_function() {
        cin.tie(0); ios::sync_with_stdio(false);
        cout << setprecision(15) << fixed;
        // #define endl "\n"
    }
} before_main_function;
//------------------8<------------------------------------8<--------------------


struct Point {
    int x;
    int y;
};

template <class P>
vector<P> convex_hull(vector<P> points) {
    int N = points.size();
    assert(N >= 2);
    sort(begin(points), end(points), [](const P& l, const P& r) { return (l.y == r.y) ? (l.x < r.x) : (l.y < r.y); });
    stack<P> left, right;

    auto tmp = [&](bool construct_left) {
        auto& out = (construct_left ? left : right);
        stack<pair<int, int>> arg;

        out.push(points[0]);
        out.push(points[1]);
        arg.push({points[1].x - points[0].x, points[1].y - points[0].y});
        for (int i = 2; i < N; i++) {
            int dx, dy;
            while (1) {
                P last = out.top();
                dx = points[i].x - last.x, dy = points[i].y - last.y;
                if (arg.empty()) break;
                int numer = arg.top().first, denom = arg.top().second;
                if (construct_left && dx * denom < dy * numer) {
                    arg.pop(); out.pop();
                } else if (!construct_left && dx * denom > dy * numer) {
                    arg.pop(); out.pop();
                } else {
                    break;
                }
            }
            arg.push({dx, dy});
            out.push(points[i]);
        }
    };
    tmp(false);
    tmp(true);

    vector<P> ret;
    ret.reserve(left.size() + right.size());
    while (!right.empty()) {
        auto& p = right.top(); right.pop();
        ret.push_back(p);
    }
    reverse(begin(ret), end(ret));
    left.pop();
    while (left.size() > 1) {
        auto& p = left.top(); left.pop();
        ret.push_back(p);
    }
    return ret;
}

signed main() {
    int N;
    cin >> N;
    vector<Point> p(N);
    REP(i, N) {
        int x, y;
        cin >> x >> y;
        p[i] = Point{x, y};
    }

    auto ch = convex_hull(p);
    
    cout << SZ(ch) << endl;
    FORE(p, ch) {
        cout << p.x << " " << p.y << endl;
    }

    return (0^_^0);
}




Measured memory_bytes: 8192