#include<stdio.h>
 FILE *fp=fopen("video.in","r");
 
 int main()
 {
 	int
 	n,xx[400],yy[400],i,dirx,diry,px,py,xmin,ymin,xmax,ymax,count=0;
 	while(1)
 	{
 		fscanf(fp," %d",&n);
 		if(!n) break;
 		printf("Floor #%d\nSurveillance is ",++count);
 		for(i=0;i<n;i++) 	fscanf(fp," %d %d",&xx[i],&yy[i]);
 			px=xx[n]=xx[0];
 			py=yy[n]=yy[0];
 			n++;
 			xmin=ymin=-1234567890;
 			xmax=ymax=1234567890;
 			
 			for(i=1;i<=n;i++)
 			{
 				dirx=-xx[i]+px;
 				diry=-yy[i]+py;
 				if(dirx>0 && ymin<py) ymin=py;
 				if(dirx<0 && ymax>py) ymax=py;
 				if(diry>0 && xmax>px) xmax=px;
 				if(diry<0 && xmin<px) xmin=px;
 				px=xx[i]; py=yy[i];
 			}
 			if(xmin<=xmax && ymin<=ymax) puts("possible.\n");
 			else puts("impossible.\n");
 	}
 	return 0;
 }