#include<stdio.h>
#include<stdlib.h>
	struct moje{
		int x,y;
	};
int porovnejx(const void *x_1,const void *x_2 )
	{	moje *x1,*x2;
		x1 = (moje *) x_1;
		x2 = (moje *) x_2;
		
		if( x1->x < x2->x) return -1;
		if((x1->x == x2->x) && (x1->y < x2->y)) return -1;
		if((x1->x == x2->x) && (x1->y > x2->y)) return 1;
		if((x1->x == x2->x) && (x1->y == x2->y)) return 0;
		
		if(x1->x > x2->x) return 1;
	
	};

int porovnejy(const void *x_1,const void *x_2 )
	{	moje *x1,*x2;
		x1 = (moje *) x_1;
		x2 = (moje *) x_2;
		
		if( x1->y < x2->y) return -1;
		if((x1->y == x2->y) && (x1->x < x2->x)) return -1;
		if((x1->y == x2->y) && (x1->x > x2->x)) return 1;
		if((x1->y == x2->y) && (x1->x == x2->x)) return 0;
		
		if(x1->y > x2->y) return 1;
	
	};

int main(){
	int p  = 1,i,vysl;
	moje pole[10001]; 
	int p1,p2; 

	scanf("%d\n",&p);
	while(p){
		vysl = 0;
		 
		for(i = 0; i < p; i++){
			scanf("%d %d\n",&p1,&p2);
			pole[i].x = p1;
			pole[i].y = p2;
		};
	//	for(i = 0; i< p; i++) printf("%d %d\n",pole[i].x,pole[i].y);
		qsort(pole,p,sizeof(moje),&porovnejx );
		for( i = 0; i < p; i=i+2) vysl += pole[i+1].y - pole[i].y;
		
		qsort(pole,p,sizeof(moje),&porovnejy );
		for( i = 0; i < p; i=i+2) vysl += pole[i+1].x - pole[i].x;
		
		scanf("%d\n",&p);
		
		
		//vysl += 2*(maxx - minx);
		printf("The length of the fence will be %d units.\n",vysl);
	};
	return 0;
}