> 
> #include<stdio.h>
> #define ABS(x) (x)>0?(x):(-(x))
> typedef struct
> {
> 	int x;
> 	int y;
> 	int num;
> }post;
> 
> void main()
> {
> 	long i,j,n,l,k;
> 	post p[10000],temp;
> 	while(1)
> 	{
> 	    scanf("%ld",&n);
> 		if(n==0)break;
> 	    for(l=0,k=0,i=0;i<n;i++)
> 		{
> 		    scanf("%d%d",&p[i].x,&p[i].y);
> 		    p[i].num=0;
> 		    for(j=k;j<i;j++)
> 			{
> 			    if(p[i].x==p[j].x){l+=ABS(p[i].y-p[j].y);p[i].num++;p[j].num++;}
> 			    else if(p[i].y==p[j].y){l+=ABS(p[i].x-p[j].x);p[i].num++;p[j].num++;}
> 			    if(p[j].num==2){temp=p[j];p[j]=p[k];p[k]=temp;k++;}
> 			    if(p[i].num==2){temp=p[i];p[i]=p[k];p[k]=temp;k++;break;}
> 			}
> 		}
> 		printf("\nThe length of the fence will be %d units.\n",l);
> 	}
> }