UVA 10589 (AREA)

/***
	Md. Nazmul Hasan
	Shahjalal University of Science & Technology,Sylhet.
	hasan08sust@gmail.com
	***/
	#include<iostream>
	#include<cstdio>
	#include<stack>
	#include<queue>
	#include<map>
	#include<vector>
	#include<algorithm>
	#include<cstring>
	#include<sstream>
	#include<cmath>
	#include <iomanip>
	using namespace std ;
	typedef long long ll ;
	typedef int in ;
	typedef unsigned long long ull ;
	const double pi = 2*acos(0) ;
	#define maxi 40000
	#define pf printf
	#define sc scanf
	#define pb push_back
	#define MEM(x,y) (memset((x),(y),sizeof(x)))
	#define MIN(x,y) ((x) < (y) ? (x) : (y))
	#define MAX(x,y) ((x) > (y) ? (x) : (y))
	#define load(array,size) for(int i=0 ; i<size ; i++) cin>>array[i] ;
	#define new_line pf("\n")
	#define clear_data(array) memset(array,0,sizeof(array))
	#define highest_int 2147483647
	double dist(double x, double y, double x1, double y1){
	return sqrt((x1-x)*(x1-x) + (y1-y)*(y1-y));
	}
	bool is_stripped(double x, double y, double a){
	if(dist(0,0,x,y) > a)
	return false;
	if(dist(0,a,x,y) > a)
	return false;
	if(dist(a,0,x,y) > a)
	return false;
	if(dist(a,a,x,y) > a)
	return false;
	return true;
	}
	int main()
	{
	int n,m;
	double x,y,a;
	while(sc("%d %lf",&n,&a)){
	if(n==0)
	break;
	m =0;
	for(int i=0 ; i<n ; i++){
	sc("%lf %lf",&x,&y);
	if(is_stripped(x,y,a)){
	m++;
	}
	}
	double area = ((m*1.0)*a*a)/(n*1.0) ;
	pf("%.5lf\n",area);
	}
	return 0;
	}