import java.awt.geom.*;
import java.io.InputStreamReader;
import java.io.BufferedReader;

public class aa {
	public static void main(String[] args) throws Exception {
		String l;
		BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
		while ((l=r.readLine())!=null) {
			int cnt = Integer.parseInt(l);
			if (cnt==0) break;
			GeneralPath path = new GeneralPath();
			int minx = Integer.MAX_VALUE,miny=Integer.MAX_VALUE,maxx=Integer.MIN_VALUE,maxy=Integer.MIN_VALUE;
			for (int i=0;i<cnt;i++) {
				String c = r.readLine();
				int sp = c.indexOf(' ');
				int x = Integer.parseInt(c.substring(0,sp))*100;
				int y = Integer.parseInt(c.substring(sp+1))*100;
				minx = Math.min(minx,x);
				maxx = Math.max(maxx,x);
				miny = Math.min(miny,y);
				maxy = Math.max(maxy,y);
				if (i==0) path.moveTo(x,y);
				else path.lineTo(x,y);
			}
			path.closePath();
			int areas = 0;
			//System.out.println(""+minx+","+miny+","+maxx+","+maxy);
			for (int x=minx;x<maxx;x+=100) {
				for (int y=miny;y<maxy;y+=100) {
					if (path.contains(x+1,y+1) && path.contains(x+99,y+1) && path.contains(x+1,y+99) && path.contains(x+99,y+99)) areas++;
				}
			}
			System.out.println(areas);
		}
	}
}