#include<iostream>
#include<vector>
#include<algorithm>
#include<math.h>
using namespace std;

struct Post;

struct Cesta
{
	Post* kam;
	bool pouzita;	
	
	Cesta(Post *p):kam(p),pouzita(false){}	
};

struct Post
{
	int x;
	int y;
	bool boltu;
	
	Post(int xx, int yy):x(xx),y(yy),boltu(false){}
	
	Cesta* 	cesta[2][2];
};

bool podla_xy(const Post* a, const Post* b)
{
	if(a->x < b->x)
		return true;
	if(a->x == b->x && a->y < b->y)
		return true;
	return false;
};


bool podla_yx(const Post* a, const Post* b)
{
	if(a->y < b->y)
		return true;
	if(a->y == b->y && a->x < b->x)
		return true;
	return false;
};

vector<Post> post;
vector<Post*> ukpost;

int main()
{
	while(1)
	{
		int p;
		cin>>p;
		if(p==0)
			return 0;
		post.clear();
		ukpost.clear();
		
		for(int i=0;i<p;i++)
		{
			int x,y;
			cin >> x >> y;
			post.push_back(Post(x,y));			
		}		
		
		for(int i=0;i<p;i++)
			ukpost.push_back( &post[i] );
		
		sort(ukpost.begin(), ukpost.end(), podla_xy );
		
		for(int i=0;i<p;i++)
		{
			//cout << "Bod " << ukpost[i]->x << " "<< ukpost[i]->y << ":" << endl;
						
			if(i>0 && ukpost[i-1]->x == ukpost[i]->x )
			{
				ukpost[i]->cesta[0][0] = new Cesta(ukpost[i-1]);
			//	cout<<"hore je"<<endl;
			}
			else 	ukpost[i]->cesta[0][0] = 0;
				
			if(i<p-1 && ukpost[i+1]->x == ukpost[i]->x )
			{
				ukpost[i]->cesta[0][1] = new Cesta(ukpost[i+1]);
			//	cout<<"dole je"<<endl;
			}
			else	ukpost[i]->cesta[0][1] = 0;
			
			
		}
		
		sort(ukpost.begin(), ukpost.end(), podla_yx );
		
		for(int i=0;i<p;i++)
		{
			//cout << "Bod " << ukpost[i]->x << " "<< ukpost[i]->y << ":" << endl;
			
			if(i>0 && ukpost[i-1]->y == ukpost[i]->y )
			{
				ukpost[i]->cesta[1][1] = new Cesta(ukpost[i-1]);
			//	cout<<"vlavo je"<<endl;
			}
			else	ukpost[i]->cesta[1][1] =0;
				
			if(i<p-1 && ukpost[i+1]->y == ukpost[i]->y )
			{
				ukpost[i]->cesta[1][0] = new Cesta(ukpost[i+1]);
			//	cout<<"vpravo je"<<endl;
			}
			else 	ukpost[i]->cesta[1][0] = 0;			
		}
		
		sort(ukpost.begin(), ukpost.end(), podla_xy );
		
		Post* kdesme = ukpost[0];
		
		int smer = 1;
		int dlzka=0;
		
		while(1)
		{
			//cout << "Sme v "<< kdesme->x << " "<< kdesme->y ;
			Post *oldkdesme = kdesme;
			if( kdesme->cesta[smer][0] !=0 && kdesme->cesta[smer][0]->pouzita==false && kdesme->cesta[smer][0]->kam->boltu==false)
			{
				Post* kam = kdesme->cesta[smer][0]->kam;				
				kdesme->cesta[smer][0]->pouzita=true;
				kam->cesta[smer][1]->pouzita=true;
				
				kdesme=kam;
				kam->boltu = true;

				//cout<< " ideme "  << ((smer==0)?"hore":"doprava") <<endl;				
			}
			else 
			if( kdesme->cesta[smer][1] !=0 && kdesme->cesta[smer][1]->pouzita==false && kdesme->cesta[smer][1]->kam->boltu==false)
			{
				Post* kam = kdesme->cesta[smer][1]->kam;
				kdesme->cesta[smer][1]->pouzita=true;
				kam->cesta[smer][0]->pouzita=true;
				
				kdesme=kam;	
				//cout<< " ideme "  << ((smer==0)?"dole":"dolava") <<endl;
				kam->boltu = true;								
			}
			else
				break;
				
			
			dlzka+=abs(oldkdesme->x - kdesme->x);
			dlzka+=abs(oldkdesme->y - kdesme->y);
			smer=(smer+1)%2;
		}
		
		cout<<"The length of fence will be "<<dlzka<<" units."<<endl;	
		

	}
	return 0;
}