#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <assert.h>
#include <limits.h>
#include <math.h>

#include <iostream.h>
#include <fstream.h>
#include <strstream.h>
#include <iomanip.h>

const char* inname = "video.in";

#ifdef TUMTEST
#define DBG cerr
#else
#define DBG if (0) cerr
#endif

ifstream in(inname);
#define out cout
FILE* fin;

template <class T>
T min(T a, T b)
{
  return (a < b) ? a : b;
}

template <class T>
T max(T a, T b)
{
  return (a > b) ? a : b;
}


#define MAXL 50

template<class T>
class List {
public:
  int first, last;
  T buffer[MAXL];

  List() : first(0), last(0) { }

  void clear() { first = last = 0; }

  int count() { return (last - first + MAXL) % MAXL; }

  int append(const T &t) {
    int i = last;
    buffer[last] = t;
    last = (last + 1) %MAXL;
    return i;
  }

  void remove(int i) {
    int j = (first + i) % MAXL, k = (j + 1) % MAXL;

    while(k != last) {
      buffer[j] = buffer[k];
      j = (j + 1) % MAXL;
      k = (k + 1) % MAXL;
    }
    last = (last - 1 + MAXL) % MAXL;
  }

  T &operator[](int i) { return buffer[(first + i) % MAXL]; }

  int index(const T &t) {
    for(int i = first; i != last; i = (i + 1) % MAXL)
      if(buffer[i] == t)
	return i;
    return -1;
  }
};

int n;

bool checkSurv()
{
  bool fail=false;
  double minX, minY;
  minX = minY = -INT_MAX;
  double maxX, maxY;
  maxX = maxY = INT_MAX;
  double x1, y1, x2, y2;
  double xs, ys;
  in >> x1 >> y1;
  xs = x1;
  ys = y1;
  for (int i = 1; i <= n; i++) {
    if (i == n) {
      x2 = xs; y2 = ys;
    }
    else {
      in >> x2 >> y2;
    }
    if (x1 == x2) {
      if (y1 < y2) {
	minX = max(minX, x1);
      }
      else {
	maxX = min(maxX, x1);
      }
    }
    else {
      if (x1 < x2) {
	maxY = min(maxY, y1);
      }
      else {
	minY = max(minY, y1);
      }
    }
    if (minY > maxY ||
	minX > maxX) {
      fail = true;
    }
    x1 = x2; y1 = y2;
  }
  DBG << "** " << minX << " " << maxX << " " << minY << " " << maxY << endl;
  return !fail;
}

int main()
{
  int cnt = 1;
  fin = fopen(inname, "r");
  while (1) {
    in >> n;
    DBG << n << endl;
    if (n ==0) break;
    out << "Floor #" << cnt++ << endl;
    out << "Surveillance is ";
    if (checkSurv()) {
      out << "possible." << endl;
    }
    else {
      out << "impossible." << endl;
    }
  }
  return 0;
}