import java.util.Collections;
import java.util.List;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;


class Usecka implements Comparable<Usecka>
{
	int x1, x2, y1, y2, xOld;
	double a, b, c;
	int index;
	
	Usecka(int x1,  int y1, int x2, int y2, int index)
	{
		this.xOld = x1;
		this.index = index;
		if(x1>x2)
		{
			this.x2 = x1;
			this.x1 = x2;
			this.y2 = y1;
			this.y1 = y2;
		}
		else
		{
			this.x1 = x1;
			this.x2 = x2;
			this.y1 = y1;
			this.y2 = y2;
			
		}

		a = y1 - y2;
		b = x2 - x1;
		c = x1*y2 - x2*y1;
	}
	
	public int compareTo(Usecka arg0) {
		
		return x1 - arg0.x1;
	}
}

public class polygon {
	
	public static void main(String[] args) throws Exception
	{
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		
		while(true)
		{
			String s = in.readLine();
			int usecek = Integer.valueOf(s);
			if(usecek==0)
				break;
			List<Usecka> usecky = new ArrayList<Usecka>();
			String ssOld[] = in.readLine().split(" ");
			for(int i=1; i<usecek; i++)
			{
				s = in.readLine();
				String ss[] = s.split(" ");
				Usecka usecka = new Usecka(Integer.valueOf(ssOld[0]), Integer.valueOf(ssOld[1]), Integer.valueOf(ss[0]), Integer.valueOf(ss[1]), i-1);
				ssOld = ss;
				usecky.add(usecka);
			}
			Usecka usecka = new Usecka(Integer.valueOf(ssOld[0]), Integer.valueOf(ssOld[1]), usecky.get(0).xOld, usecky.get(0).y1, usecek-1);
			usecky.add(usecka);
			Collections.sort(usecky);
			//System.out.println(Arrays.toString(koefA));
			//System.out.println(Arrays.toString(koefB));
			//System.out.println(Arrays.toString(koefC));
			
			boolean prusecik = false;
			konec:
			for(int i=0; i<usecky.size()-1; i++)
			{
				Usecka usecka1 = usecky.get(i);
				for(int j=i+1; j<usecky.size(); j++)
				{
					Usecka usecka2 = usecky.get(j);
					if(usecka1.x2<usecka2.x1)
						break;
					double x = usecka1.b * usecka2.c - usecka1.c * usecka2.b;
					double y = usecka1.c * usecka2.a - usecka1.a * usecka2.c;
					double w = usecka1.a * usecka2.b - usecka1.b * usecka2.a;
					//todo
					if(w==0)
					{
						if (Math.abs(usecka1.a * usecka2.x1 + usecka1.b * usecka2.y1 + usecka1.c) < 0.0001)
						{
							prusecik = true;
							break konec;
						}
						else continue;
					}
					x /= w; 
					y /= w; 
					//System.out.println(x+" "+y+" "+w+"    "+useckyX[i]+" "+useckyY[i]+"   "+useckyX[j]+" "+useckyY[j]+"   "+x+" "+y);
					double x1 = usecka1.x1;
					double x2 = usecka1.x2;
						if(x<=x2 && x>=x1 && (usecka1.index-usecka2.index)>1 && (usecka1.index-usecka2.index)!=usecky.size())
						{
							x1 = usecka2.x1;
							x2 = usecka2.x2;
							if(x<=x2 && x>=x1)
							{
								prusecik = true;
								break konec;
							}
						}
				}
			}
			if(!prusecik)
				System.out.println("YES");
			else
				System.out.println("NO");
		}
	}

}