#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<iomanip>
#include<complex>
#include<cstdio>
#include<vector>
#include<queue>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef stack<int> SI;
typedef queue<int> QI;
typedef list<int> LI;
typedef pair<int,int> PII;
typedef long long LL;

#define d(x)  cout<<#x<<" = "<<(x)<<endl;
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define EMP empty()
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define REACH(i,c) for(typeof((c).rbegin()) i=(c).rbegin(); i!=(c).rend(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c,n) sort(c,c+n)
#define VSORT(c) sort((c).begin(),(c).end())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define DFOR(i,b,a) for(int i=(b)-1;i>=(a);--i)
#define DREP(i,n) DFOR(i,n,0)
#define INF 1000000000
#define PI  acos(-1.0)
////////////////////////////////////////////////
#define EPS (1e-10)
#define equals(a,b) (fabs((a)-(b))<EPS)

/*????????????(??§?¨?)????????????*/
class Vector
{
public:
	double x,y;
	Vector(double x=0,double y=0):x(x),y(y){}
	
	Vector operator + (Vector p){return Vector(x+p.x,y+p.y);}
	Vector operator - (Vector p){return Vector(x-p.x,y-p.y);}
	Vector operator * (double a){return Vector(x*a,y*a);}
	Vector operator / (double a){return Vector(x/a,y/a);}
	
	double abs(){return sqrt(norm());}
	double norm(){return x*x+y*y;}
	
	bool operator <  (const Vector &p)const{return x!=p.x?x<p.x:y<p.y;}
	bool operator == (const Vector &p)const{return fabs(x-p.x)<EPS && fabs(y-p.y<EPS);}
};

/*??´???????????????*/
class Line
{
public:
	Vector p,q;
	Line(Vector p=Vector(),Vector q=Vector()):p(p),q(q){}
};

/*???????????????*/
class Circle
{
public:
	Vector c;
	double r;
	Circle(Vector c=Vector(),double r=0.0):c(c),r(r){}
};

/*????§???¢??????*/
typedef vector<Vector> Polygon;

/*???????????????????¬????????????§??????*/
double dot(Vector a,Vector b){return a.x*b.x+a.y*b.y;}
double cross(Vector a,Vector b){return a.x*b.y-b.x*a.y;}

/*??´??????????°???±*/
Vector project(Line l,Vector p)
{
	Vector base=l.q-l.p;
	double r=dot(p-l.p,base)/base.norm();
	return l.p+base*r;
}

/*????????¨??????????????¢????????????*/
int ccw(Vector p0,Vector p1,Vector p2)
{
	Vector a=p1-p0;
	Vector b=p2-p0;
	if(cross(a,b)>EPS)return 1;//???????¨???????
	if(cross(a,b)<-EPS)return -1;//????¨???????
	if(dot(a,b)<-EPS)return 2;//p0?????????
	if(a.norm()<b.norm())return -2;//p1????\\
	return 0;//?????????
}

/*?????????????????????*/
bool intersect(Vector p0,Vector p1,Vector p2,Vector p3)
{
	return (ccw(p0,p1,p2)*ccw(p0,p1,p3)<=0&&ccw(p2,p3,p0)*ccw(p2,p3,p1)<=0);
}

/*??´?????¨??´????????????*/
Vector LLcross(Vector p0,Vector p1,Vector p2,Vector p3)
{
	double d1=cross(p3-p2,p0-p2);
	double d2=cross(p3-p2,p1-p3);
	return p0+(p1-p0)*(d1/(d1+d2));
}

/*?????¨??´????????????*/
pair<Vector,Vector> CLcross(Circle c,Line l)
{
	Vector pr=project(l,c.c);
	Vector e=(l.q-l.p)/(l.q-l.p).abs();
	double base=sqrt(c.r*c.r-(pr-c.c).norm());
	return make_pair(pr+e*base,pr-e*base);
}

/*?????¨????????????*/
double arg(Vector p){return atan2(p.y,p.x);}
Vector pol(double a,double r){return Vector(cos(r)*a,sin(r)*a);}
pair<Vector,Vector> CCcross(Circle c1,Circle 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+pol(c1.r,t+a),c1.c+pol(c1.r,t-a));
}

/*????§???¢??????????????????????????????*/
int contain(Polygon g,Vector p)
{
	int n=g.size();
	bool x=false;
	for(int i=0;i<n;i++)
	{
		Vector a=g[i]-p,b=g[(i+1)%n]-p;
		if(abs(cross(a,b))<EPS&&dot(a,b)<EPS)return 1;//??????
		if(a.y>b.y)swap(a,b);
		if(a.y<EPS&&EPS<b.y&&cross(a,b)>EPS)x=!x;
	}
	return (x?2:0);//?????????2?????????0
}

/*??????(Andrew)*/
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&&ccw(u[n-2],u[n-1],s[i])>=0;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&&ccw(l[n-2],l[n-1],s[i])>=0;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;
}


//cout<<fixed<<setprecision(10);
////////////////////////////////////////////////
int main()
{
	int n;cin>>n;
	Polygon s;
	REP(i,n)
	{
		Vector a;cin>>a.x>>a.y;
		s.PB(a);
	}
	Polygon l=AndrewScan(s);
	cout<<SZ(l)<<endl;
	int m=0;
	Vector min=l[0];
	REP(i,SZ(l))
	{
		if(l[i].y<=min.y)
		{
			if(l[i].y==min.y)
			{
				if(l[i].x<min.x)
				{
					m=i;
				}
			}
			else
			{
				min.y=l[i].y;
				m=i;
			}
		}
	}
	REP(i,SZ(l))
	{
		cout<<l[m%SZ(l)].x<<" "<<l[m%SZ(l)].y<<endl;
		m++;
	}
	return 0;
}

Measured memory_bytes: 9356