// Gokuri

#include <iostream>
#include <fstream>
#include <vector>
#include <deque>
#include <map>
#include <set>
#include <string>
#include <cmath>
#include <cctype>
#include <complex>
#include <cfloat>

using namespace std;

#define FNAME "video.txt"
#define fin cin

#define EPSILON 1.0E-6

typedef complex<int>  point;
typedef vector<point> polygon;
struct area {
  int xmin, ymin;
  int xmax, ymax;
};

bool solve(const polygon& p)
{
  area a;
  a.xmin = a.ymin = INT_MAX;
  a.xmax = a.ymax = INT_MIN;
  for(int i = 0; i < p.size(); i++) {
    const point pt = p[i];
    if(pt.real() < a.xmin) a.xmin = pt.real();
    if(pt.real() > a.xmax) a.xmax = pt.real();
    if(pt.imag() < a.ymin) a.ymin = pt.imag();
    if(pt.imag() > a.ymax) a.ymax = pt.imag();
  }
  
  for(int i = 0; i < p.size(); i++) {
    const point p1 = p[i], p2 = p[(i + 1) % p.size()];
    if(p1.real() == p2.real()) {
      // tate
      if(p1.imag() > p2.imag()) {
        if(a.xmax > p1.real()) a.xmax = p1.real();
      } else if(p1.imag() < p2.imag()) {
        if(a.xmin < p1.real()) a.xmin = p1.real();
      } else
        abort();
    } else if(p1.imag() == p2.imag()) {
      // yoko
      if(p1.real() < p2.real()) {
        if(a.ymax > p1.imag()) a.ymax = p1.imag();
      } else if(p1.real() > p2.real()) {
        if(a.ymin < p1.imag()) a.ymin = p1.imag();
      } else
        abort();
    } else
      abort();
  }
  
  if(a.xmax >= a.xmin && a.ymax >= a.ymin)
    return true;
  else
    return false;
}

int main(void)
{
  ifstream fin(FNAME);
  if (!fin) { return 1; }

  // INPUT HERE
  int ncase = 0;
  int np;
  while(cin >> np, np) {
    polygon pol;
    while(np--) {
      int x, y;
      cin >> x >> y;
      pol.push_back(point(x, y));
    }
    
    cout << "Floor #" << ++ncase << endl;
    cout << "Surveillance is " << (solve(pol) ? "possible" : "impossible")
      << "." << endl;
    cout << endl;
  }
  
  return 0;
}