#include<stdio.h>
	struct moje{
		bool b;
		int max,min;
	};

int main(){
	int p  = 1,minx =0, maxx = 10000,i,vysl;
	moje pole[10001]; 
	for (i = 0; i < 10001; i ++) pole[i].b = 0;
	int p1,p2; 

	scanf("%d\n",&p);
	while(p){
		vysl = 0;
		maxx = 0;minx = 10000; 
		for(i = 0; i < p; i++){
			scanf("%d %d\n",&p1,&p2);
//			printf("%d %d\n",p1,p2);
			if(!pole[p1].b) {
				pole[p1].b = 1;
				pole[p1].max = p2;
				pole[p1].min = p2;
			}else {
				if (p2 < pole[p1].min) pole[p1].min = p2;
				if (p2 > pole[p1].max) pole[p1].max = p2;
			}
				
			if(p1 < minx) minx = p1;
			if(p1 > maxx) maxx = p1;
			
		};
		
		scanf("%d\n",&p);
		
		for(i = 0; i <= 10000; i++) {
			if (pole[i].b){
				vysl+= pole[i].max - pole[i].min;
				pole[i].b = 0;
			}
		}
		vysl += 2*(maxx - minx);
		printf("The length of the fence will be %d units.\n",vysl);
	};
	return 0;
}