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

int sortXY(const void * _a, const void * _b)
{
    int *a = (int*)_a;
    int *b = (int*)_b;
    if(a[0] < b[0])
	return -1;
    else if (a[0] > b[0])
	return 1;
    else
	return a[1] - b[1];
}

int sortYX(const void *_a, const void *_b)
{
    int *a = (int*)_a;
    int *b = (int*)_b;
    if(a[1] < b[1])
	return -1;
    else if (a[1] > b[1])
	return 1;
    else
	return a[0] - b[0];
}


int secti(int (*posts)[2], int P, int C)
{
    int F;
    
    for (F = 0; P--; P--)
	F += posts[P][C] - posts[P - 1][C];
    
    return F;
}

int main()
{
    int posts[100000][2];
    int P;
    int F;
    int N;

    scanf("%d", &P);
    while (P)
    {
	N = P;
	
	while (P--)
            scanf("%d %d", posts[P], posts[P] + 1);
	
	F = 0;

	qsort(posts, N, 2*sizeof(int), sortYX);
	F += secti(posts, N, 0);

	qsort(posts, N, 2*sizeof(int), sortXY);
	F += secti(posts, N, 1);

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