#include <vector>
#include <iostream>
#include <cmath>
using namespace std;

const int MAX = 40000;

struct Bod
{
  double x;
  double y;
};

struct Rovnice
{
  double a;
  double b;
};

struct Primka
{
  Bod start;
  Bod konec;
  Rovnice rovnice;
  
  bool leziNa(double px, double py) const
  {
    if(start.x > konec.x)
    {
      if(((double)start.x < px) || ((double)konec.x > px)) return false;
      if(start.y > konec.y)
      {
        if(((double)start.y < py) || ((double)konec.y > py)) return false;
      }
      else
      {
        if(((double)start.y > py) || ((double)konec.y < py)) return false;
      }
    }
    else
    {
      if(((double)start.x > px) || ((double)konec.x < px)) return false;
      if(start.y > konec.y)
      {
        if(((double)start.y < py) || ((double)konec.y > py)) return false;
      }
      else
      {
        if(((double)start.y > py) || ((double)konec.y < py)) return false;
      }
    }
    return true;
  }
  
  void rovnice_primky()
  {
    double a = konec.y - start.y;
    double b = start.x - konec.x;
    rovnice.a = -(a / b);
    rovnice.b = -((-a * start.x - b * start.y) / b);
    //rovnice.a = (double)(start.x - konec.x) / (double)(start.y - konec.y);
    //rovnice.b = (double)(((-start.x + konec.x) * start.x) + ((-start.y + konec.y) * start.y)) / (double)(start.y - konec.y);
    //cout << "A:" << rovnice.a << "; B:" << rovnice.b << endl;
  }
  
  bool prusecik(const Primka &p) const
  {
    // Prusecik primek
    double px = (double)(p.rovnice.b - rovnice.b) / (double)(rovnice.a - p.rovnice.a);
    double py = (double)rovnice.a * px + (double)rovnice.b;
    //cout << "X:" << px << "; Y:" << py << endl;
    if(!leziNa(px, py)) return false;
    if(!p.leziNa(px, py)) return false;
    return true;
  }
};

bool kriziSe(Primka *primky, int p, int n) // p je aktualni primka
{
  if(p < 3) return false;
  // hledam pruseciky
  for(int i = p - 2; i >= n; i--)
  {
    if(primky[i].prusecik(primky[p]))
    {
      return true;
    }
  }
  return false;
}

int main()
{
  /*
  Primka p1, p2;
  p1.start.x=1; p1.start.y=6;
  p1.konec.x=6; p1.konec.y=1;
  p2.start.x=2; p2.start.y=3;
  p2.konec.x=9; p2.konec.y=4;
  p1.rovnice_primky();
  p2.rovnice_primky();
  if(p1.prusecik(p2))
    cout << "PRUSECIK" << endl;
  else
    cout << "HOVNO" << endl;
  return 1;
  */
  int n;
  int p;
  Primka *primky = new Primka[MAX+1];
  bool krizi;
  while(1)
  {
    cin >> n;
    if(n == 0) break;
    p = 0;
    krizi = false;
    cin >> primky[p].start.x >> primky[p].start.y;
    for(int i = 1; i < n; i++)
    {
      cin >> primky[p].konec.x >> primky[p].konec.y;
      if(!krizi)
      {
        primky[p].rovnice_primky();
        krizi = kriziSe(primky, p, 0);
        // konec stary primky je zacatek novy primky
        primky[p+1].start.x = primky[p].konec.x;
        primky[p+1].start.y = primky[p].konec.y;
        p++;
      }
    }
    if(!krizi)
    {
      // spojit posledni bod s prvnim
      primky[p].konec.x = primky[0].start.x;
      primky[p].konec.y = primky[0].start.y;
      primky[p].rovnice_primky();
      krizi = kriziSe(primky, p, 1);
      p++;
    }
    //
    if(krizi)
      cout << "NO\n";
    else
      cout << "YES\n";
  }
  delete [] primky;
  return 0;
}