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

__extension__ typedef unsigned long long res_t;

#define MAXP 128000

static unsigned points[MAXP][2];
static size_t column;
unsigned p;

static int
cmp (const void *xa, const void *xb)
{
  const unsigned *a, *b;

  a = xa;
  b = xb;
  if (a[column] > b[column])
    return 1;
  if (a[column] < b[column])
    return -1;
  if (a[1 - column] > b[1 - column])
    return 1;
  if (a[1 - column] < b[1 - column])
    return -1;
  return 0;
}

__inline__ static res_t
count (void)
{
  size_t i;
  res_t r;

  r = 0;
  for (i = 0; i < p - 1; i++)
    {
      if (points[i][column] == points[i + 1][column])
	{
	  r += points[i + 1][1 - column] - points[i][1 - column];
	  i++;
	}
    }
  return r;
}

int
main (void)
{
  for (;;)
    {
      size_t i;
      res_t res;
      
      scanf ("%u", &p);
      if (p == 0)
	break;
      for (i = 0; i < p; i++)
	scanf ("%u%u", points[i], points[i] + 1);
      res = 0;
      for (column = 0; column < 2; column++)
	{
	  qsort (points, p, sizeof (*points), cmp);
	  res += count ();
	}
      printf ("The length of the fence will be %llu units.\n", res);
    }
  return EXIT_SUCCESS;
}