#include <stdio.h>
#include <stdlib.h>

#define MAX 100000

struct bod
{
	int x, y;
};

int  compare1(const void* a, const void* b)
{
	if( ((const bod*)a)->x > ((const bod*)b)->x ) return 1;
	if (((bod*)a)->x == ((bod*)b)->x )
	{
		if ( ((bod*)a)->y > ((bod*)b)->y ){
			return 1;
		} else if (((bod*)a)->y == ((bod*)b)->y ){
			return 0;
		} else {return -1; }
	} else { return -1; }
}
int  compare2(const void* a, const void* b)
{
	if( ((bod*)a)->y > ((bod*)b)->y ) return 1;
	if (((bod*)a)->y == ((bod*)b)->y )
	{
		if( ((bod*)a)->x > ((bod*)b)->x ){
			return 1;
		} else if (( (bod*)a)->x == ((bod*)b)->x ){
			return 0;
		} else {return -1; }} else { return -1; }

}

int soucet;

int main()
{
	bod pole[MAX];
	int i, j, count;
	while(scanf("%d", &count), count)
	{
		soucet = 0;
		for(i = 0; i < count; i++)
			scanf("%d %d", &pole[i].x, &pole[i].y);
		qsort(pole, count, sizeof(bod), compare1);
		for (i=0; i<count; i +=2 ){
			soucet += pole[i+1].y - pole[i].y;
		}
		qsort(pole, count, sizeof(bod), compare2);
		for (i=0; i<count; i +=2 ){
			soucet += pole[i+1].x - pole[i].x;
		}

	printf("The length of the fence	will be %d units.\n", soucet );
	}
	return 0;
}