content: package v110;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.StringTokenizer;
  
  public class Area_UVa10589 {
  	
  	static final double EPS = 1e-15;
  	
  	public static void main(String[] args) throws IOException {
  		
  		Scanner sc = new Scanner(System.in);
  		PrintWriter out = new PrintWriter(System.out);
  	
  		while(true)
  		{
  			int n = sc.nextInt();
  			if(n == 0) break;
  			double a = sc.nextDouble();
  			
  			Circle[] circles = new Circle[4];
  			circles[0] = new Circle(new Point(0, 0), a);
  			circles[1] = new Circle(new Point(0, a), a);
  			circles[2] = new Circle(new Point(a, 0), a);
  			circles[3] = new Circle(new Point(a, a), a);
  			int m = 0;
  			for(int i = 0; i < n; i++)
  			{
  				Point p = new Point(sc.nextDouble(), sc.nextDouble());
  				boolean inside = true;
  				for(int j = 0; j < 4 && inside; j++)
  					if(!circles[j].inside(p))
  						inside = false;
  				if(inside)
  					m++;
  			}
  			out.printf("%.5f\n",  a  * a * m / n);
  		}
  		out.flush();
  	}
  	
  	static class Point
  	{
  		double x, y;
  		
  		Point(double a, double b)
  		{
  			x = a; y = b;
  		}
  	}
  	
  	static class Circle
  	{
  		Point c;
  		double r;
  		
  		Circle(Point p, double k)
  		{
  			c = p;
  			r = k;
  		}
  		
  		boolean inside(Point p)
  		{
  			double a = (p.x - c.x) * (p.x - c.x) + (p.y - c.y) * (p.y - c.y), b = r * r;
  			
  			return a <= b + EPS;
  		}
  		
  	}
  	
  	static class Scanner 
  	{
  		StringTokenizer st;
  		BufferedReader br;
  
  		public Scanner(InputStream s){	br = new BufferedReader(new InputStreamReader(s));}
  
  		public String next() throws IOException 
  		{
  			while (st == null || !st.hasMoreTokens()) 
  				st = new StringTokenizer(br.readLine());
  			return st.nextToken();
  		}
  
  		public int nextInt() throws IOException {return Integer.parseInt(next());}
  		
  		public long nextLong() throws IOException {return Long.parseLong(next());}
  
  		public String nextLine() throws IOException {return br.readLine();}
  		
  		public double nextDouble() throws IOException
  		{
  			String x = next();
  			StringBuilder sb = new StringBuilder("0");
  			double res = 0, f = 1;
  			boolean dec = false, neg = false;
  			int start = 0;
  			if(x.charAt(0) == '-')
  			{
  				neg = true;
  				start++;
  			}
  			for(int i = start; i < x.length(); i++)
  				if(x.charAt(i) == '.')
  				{
  					res = Integer.parseInt(sb.toString());
  					sb = new StringBuilder("0");
  					dec = true;
  				}
  				else
  				{
  					sb.append(x.charAt(i));
  					if(dec)
  						f *= 10;
  				}
  			res += Integer.parseInt(sb.toString()) / f;
  			return res * (neg?-1:1);
  		}
  		
  		public boolean ready() throws IOException {return br.ready();}
  
  
  	}
  }
  