#include <iostream>
#include <cmath>
#include <cstdio>

using namespace std;

double dist(double x, double y, double x1, double y1) {
	return sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
}

bool is_striped(double x, double y, double k) {
	if (dist(0, 0, x, y) > k)
		return false;
	if (dist(0, k, x, y) > k)
		return false;
	if (dist(k, 0, x, y) > k)
		return false;
	if (dist(k, k, x, y) > k)
		return false;
	return true;
}

int main() {
	int n, i, k, m;
	double x, y;

	while (scanf("%d %d", &n, &k) && n) {
		m = 0;
		for (i = 0; i < n; i++) {
			scanf("%lf %lf", &x, &y);
			if (is_striped(x, y, k * 1.))
				m++;
		}
		printf("%.5lf\n", (m * k * k * 1.) / n);
	}

	return 0;
}