// what is matter? never mind. 
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,mmx,avx,avx2") 
#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
#define int long long
#define ull unsigned long long

using namespace std;
inline int read()
{
    char c=getchar();int x=0;bool f=0;
    for(;!isdigit(c);c=getchar())f^=!(c^45);
    for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
    if(f)x=-x;return x;
}

#define mod 998244353
struct modint{
	int x;
	modint(int o=0){x=o;}
	modint &operator = (int o){return x=o,*this;}
	modint &operator +=(modint o){return x=x+o.x>=mod?x+o.x-mod:x+o.x,*this;}
	modint &operator -=(modint o){return x=x-o.x<0?x-o.x+mod:x-o.x,*this;}
	modint &operator *=(modint o){return x=1ll*x*o.x%mod,*this;}
	modint &operator ^=(int b){
		modint a=*this,c=1;
		for(;b;b>>=1,a*=a)if(b&1)c*=a;
		return x=c.x,*this;
	}
	modint &operator /=(modint o){return *this *=o^=mod-2;}
	friend modint operator +(modint a,modint b){return a+=b;}
	friend modint operator -(modint a,modint b){return a-=b;}
	friend modint operator *(modint a,modint b){return a*=b;}
	friend modint operator /(modint a,modint b){return a/=b;}
	friend modint operator ^(modint a,int b){return a^=b;}
	friend bool operator ==(modint a,modint b){return a.x==b.x;}
	friend bool operator !=(modint a,modint b){return a.x!=b.x;}
	bool operator ! () {return !x;}
	modint operator - () {return x?mod-x:0;}
	bool operator <(const modint&b)const{return x<b.x;}
};
inline modint qpow(modint x,int y){return x^y;}

vector<modint> fac,ifac,iv;
inline void initC(int n)
{
	if(iv.empty())fac=ifac=iv=vector<modint>(2,1);
	int m=iv.size(); ++n;
	if(m>=n)return;
	iv.resize(n),fac.resize(n),ifac.resize(n);
	For(i,m,n-1){
		iv[i]=iv[mod%i]*(mod-mod/i);
		fac[i]=fac[i-1]*i,ifac[i]=ifac[i-1]*iv[i];
	}
}
inline modint C(int n,int m){
	if(m<0||n<m)return 0;
	return initC(n),fac[n]*ifac[m]*ifac[n-m];
}
inline modint sign(int n){return (n&1)?(mod-1):(1);}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,int>pii;
typedef vector<int>vi;

#define maxn 800005
#define inf 0x3f3f3f3f

struct P{
	int x,y,id;
	P(int x=0,int y=0):x(x),y(y){}
	P&operator +=(P o){return x+=o.x,y+=o.y,*this;}
	P&operator -=(P o){return x-=o.x,y-=o.y,*this;}
	P&operator *=(int o){return x*=o,y*=o,*this;}
	P&operator /=(int o){return x/=o,y/=o,*this;}
	friend P operator +(P a,P b){return a+=b;}
	friend P operator -(P a,P b){return a-=b;}
	friend P operator *(P a,int b){return a*=b;}
	friend P operator /(P a,int b){return a/=b;}
	friend bool operator <(P a,P b){return a.x==b.x?a.y<b.y:a.x<b.x;}
	friend int operator %(P a,P b){return a.x*b.x+a.y*b.y;} // dot
	friend int operator *(P a,P b){return a.x*b.y-a.y*b.x;} // cross
	
	inline double ang(){return atan2(y,x);}
	inline double l(){return sqrt((*this)*(*this));}
	
	void read(){cin>>x>>y;}
	void out(){cout<<"("<<x<<","<<y<<")"<<endl;}
};

int sgn(int x){
	return x<0?-1:(x>0);
}
int cross(P a,P b,P c){
	//(a->b) ---> (a->c)
	return (b-a)*(c-a);
}
int cmp3(P a,P b,P c){
	return sgn(cross(a,b,c));
}

int n,m;
vector<P>a,b,t;
bool vis[maxn];

vector<P>convex(vector<P>o){
	sort(o.begin(),o.end());
	int n=o.size();
	vector<P>p;
	For(i,0,n-1){
		while(p.size()>1&&(p.back()-p[p.size()-2])*(o[i]-p[p.size()-2])<=0) p.pop_back();
		p.pb(o[i]);
	}
	int m=p.size();
	Rep(i,n-2,0){
		while(p.size()>m&&(p.back()-p[p.size()-2])*(o[i]-p[p.size()-2])<=0) p.pop_back();
		if(i)p.pb(o[i]);
	}
	return p;
}

void check(vector<P>o){
	int n=o.size();
	vector<int>d(n);
	For(i,0,n-1) d[i]=cmp3(o[i],o[(i+1)%n],o[(i+2)%n]);
	For(i,0,n-1) if(d[i]!=-d[(i+1)%n]) return;
	cout<<o.size()<<"\n";
	for(auto it:o)cout<<it.x<<" "<<it.y<<"\n";
	exit(0);
}

bool in(P p,P a,P b,P c){
	return cmp3(a,b,p) && cmp3(b,c,p) && cmp3(c,a,p);
}

bool vis1[13],vis2[13];
vector<P>ans;
void dfs(int u){
	if(u==6){
		check(ans);
		return;
	}
	if(u%2==0){
		For(i,0,n-1) if(!vis1[i]) {
			vis1[i]=1;
			ans[u]=b[i];
			dfs(u+1);
			vis1[i]=0;
		}
	}else{
		For(i,0,m-1) if(!vis2[i]){
			vis2[i]=1;
			ans[u]=t[i];
			dfs(u+1);
			vis2[i]=0;
		}
	}
}

void solve3(){
//	for(auto it:b)it.out();puts("---b---");
//	for(auto it:t)it.out();puts("---t---");
	while(b.size()>6){
		n=b.size();
		bool fd=0;
		Rep(i,n-1,0){
			P A=b[(i+n-1)%n],B=b[i],C=b[(i+1)%n];
			bool ok=1;
			for(auto p:t)
				if(in(p,A,B,C)) ok=0;
			if(ok){
				For(j,i,n-2) b[j]=b[j+1];
				b.pop_back();
				fd=1;
				break;
			}
		}
		assert(fd);
	}
	n=b.size();
	m=t.size();
	ans.resize(6);
	dfs(0);
	assert(0);
}

int op[maxn];
P A,B;
vector<P>p,q;
void solve2(){
	n=b.size();
	A=t[0],B=t[1];
	int c1=0,c2=0;
	For(i,0,n-1) op[i]=cmp3(A,B,b[i]),c1+=(op[i]>0),c2+=(op[i]<0);
	if(c1<=1 || c2<=1){
		puts("-1");
		exit(0);
	}
	For(i,0,n-1) if(op[(i+n-1)%n]==-1 && op[i]==1){
		for(int j=i;op[j]==1;j=(j+1)%n) p.pb(b[j]);
		break;
	}
	For(i,0,n-1) if(op[(i+n-1)%n]==1 && op[i]==-1){
		for(int j=i;op[j]==-1;j=(j+1)%n) q.pb(b[j]);
		break;
	}
	assert(p.size()>=2 && q.size()>=2);
	P p1,p2,q1,q2;
	int np=p.size(),nq=q.size();
	int j=nq-1;
	bool ok=0;
	Rep(i,np-1,0){
		while(j>=0 && cmp3(p[i],B,q[j])>0) --j;
		if(j>=0 && cmp3(p[i],A,q[j])>0){
			p1=p[i],q1=q[j];
			ok=1;
			break;
		}
	}
	if(!ok)puts("-1"),exit(0);
	j=0;
	ok=0;
	For(i,0,nq-1){
		while(j<=np-1 && cmp3(q[i],B,p[j])<0) ++j;
		if(j<=np-1 && cmp3(q[i],A,p[j])<0){
			q2=q[i],p2=p[j];
			ok=1;
			break;
		}
	}
	if(!ok)puts("-1"),exit(0);
	vector<P>tmp={p1,A,q2,p2,B,q1};
	For(i,0,5)For(j,i+1,5)if(tmp[i].id==tmp[j].id)puts("-1"),exit(0);
	check(tmp);
	puts("-1"),exit(0);
}

signed main()
{
	n=read();
	a.resize(n);
	For(i,0,n-1)a[i].x=read(),a[i].y=read(),a[i].id=i;
	b=convex(a);
	for(auto t:b) vis[t.id]=1;
	int cnt=0;
	For(i,0,n-1)cnt+=(!vis[i]);
	if(cnt<=1){
		puts("-1");
		exit(0);
	}
	vector<P>aa;
	for(auto t:a) if(!vis[t.id] && aa.size()<3) aa.pb(t);
	::t=aa;
	if(cnt>=3) solve3();
	else solve2();
	return 0;
}
/*
6
0 0 
2 0
1 10
-10 -1
10 -1
1 1

10
5 7
6 6
8 3
2 2
4 2
3 5
7 6
10 4
1 5
9 3
1
3 7 4 8
*/