#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <string.h>

#define	INT_MAX		2147483647	
#define	INT_MIN		(-2147483647-1)	

int Xmax = INT_MAX;
int Xmin = INT_MIN;
int Ymax = INT_MAX;
int Ymin = INT_MIN;


int ver[110][2];


int main ()
{
  int i=0,j=0,k=0,n=0;
  int VX, VY;
  int possible ;
  FILE* in=fopen("video.in","r");
  
  while(fscanf(in,"%d", &n) , n!=0){
    for(i=0;i<n;i++){
      fscanf(in, "%d %d",  &(ver[i][0]), &(ver[i][1]) );
    } 
    
    ver[n][0] = ver[0][0] ;
    ver[n][1] = ver[0][1] ;
    for(i=0;i<n;i++){
      VX = ver[i+1][0] - ver[i][0];
      VY = ver[i+1][1] - ver[i][1];
      if((VX == 0) ){
	if(VY>0){
	  if(ver[i][0] > Xmin){
	    Xmin = ver[i][0];
	  }
	}else{
	  if(ver[i][0] < Xmax){
	    Xmin = ver[i][0];
	  }
	}
      }else
	if((VY == 0)){
	  if(VX>0){
	    if(ver[i][1] > Ymin){
	      Ymin = ver[i][1];
	    }
	  }else{
	    if(ver[i][1] < Ymax){
	      Ymax = ver[i][1];
	    }
	  }
	}
      
      if(  (Xmin>Xmax)  || (Ymin>Ymax) ){
	possible = 0;
	break;
      }
      
    }
    
    if( (Xmin>Xmax)  || (Ymin>Ymax)){
      printf("Surveillance is impossible.\n");
    }else{
      printf("Surveillance is possible.\n") ;   
    }
    
  }
  
  
  
  
  fclose(in);
  return 0;
}