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

typedef struct{
  int x;
  int y;
}*PBOD, BOD;


int porovnej(const void *pa, const void *pb){
  PBOD a = (PBOD) pa;
  PBOD b = (PBOD) pb;

  if ((*a).x == (*b).x)
    return ((*a).y > (*b).y);
  else
    return ((*a).x > (*b).x);
  
}
int porovnejy(const void *pa, const void *pb){
  PBOD a = (PBOD) pa;
  PBOD b = (PBOD) pb;

  if ((*a).y == (*b).y)
    return ((*a).x > (*b).x);
  else
    return ((*a).y > (*b).y);
  
}

int main(void){
  int numdeps;
  PBOD pbod;
  int i;
  int delka;

  scanf("%d\n", &numdeps);
  
  while (numdeps !=0){
    if ((pbod=malloc(sizeof(BOD)*numdeps))==NULL)
      return 1;
      

  for (i=0; i<numdeps; i++){
    scanf("%d %d\n", &pbod[i].x, &pbod[i].y);
  }
  
  delka=0;
  qsort((void*) pbod, numdeps, sizeof(BOD), porovnej);
  for (i=0; i<numdeps; i+=2)
    {
      delka+=(pbod[i+1].y - pbod[i].y);
    }

  qsort((void*) pbod, numdeps, sizeof(BOD), porovnejy);
  for (i=0; i<numdeps; i+=2)
    {
      delka+=(pbod[i+1].x - pbod[i].x);
    }
  printf("The length of the fence will be %d units.\n", delka);
  scanf("%d\n", &numdeps);
  free(pbod);
  }  
  
  return 0;
}