#include <stdio.h>

int main(void){
 int i,j,k;
 long pocet,L;
 int fx,fy,lx,ly,px,py;
 
 scanf("%ld\n",&pocet);
 while(pocet!=0){
  scanf("%d %d",&fx,&fy);
  scanf("%d %d",&lx,&ly);
  if (fx==lx) {L=((fy<ly)?(ly-fy):(fy-ly));}
  else {L=((fx<lx)?(lx-fx):(fx-lx));}
  for(i=2;i<pocet;i++){
   scanf("%d %d",&px,&py);
   if (px==lx) {
    L+=((py<ly)?(ly-py):(py-ly));
    lx=px;ly=py;
   }
   if (py==ly) {
    L+=((px<lx)?(lx-px):(px-lx));
    lx=px;ly=py;
   }
   if (px==fx) {
    L+=((py<fy)?(fy-py):(py-fy));
    fx=px;fy=py;
   }
   if (py==fy) {
    L+=((px<fx)?(fx-px):(px-fx));
    fx=px;fy=py;
   }
  }
 printf("The length of the fence will be %ld units.\n",L);
 getchar();
 getchar();
 scanf("%ld\n",&pocet);  
 } 
return 0;
}