#include<bits/stdc++.h>
using std::cin;
using std::cout;
const int N = 500005;
using ll = long long;
using u64 = unsigned long long;
using db = long double;
const db eps = 1e-10;
struct vec2 {
	db x, y;
	db abs() const { return sqrt(x * x + y * y); }
};
vec2 operator + (vec2 x, vec2 y) { return {x.x + y.x, x.y + y.y}; }
vec2 operator - (vec2 x, vec2 y) { return {x.x - y.x, x.y - y.y}; }
db operator % (vec2 x, vec2 y) { return x.x * y.x + x.y * y.y; }
db operator * (vec2 x, vec2 y) { return x.x * y.y - x.y * y.x; }
struct seg { vec2 x, y; };
db dist(seg o, vec2 x) {
	if((o.x - o.y) % (x - o.y) <= eps) return (x - o.y).abs();
	if((o.y - o.x) % (x - o.x) <= eps) return (x - o.x).abs();
	return fabs((o.x - x) * (o.y - x) / (o.x - o.y).abs());
}
int n;


db R;

int main() {
	std::ios::sync_with_stdio(false), cin.tie(0);
	cin >> n >> R;
	std::vector<vec2> a(n);
	std::vector<seg> b(n);
	for(int i = 0;i < n;++i) {
		cin >> a[i].x >> a[i].y;
	}
	for(int i = 0;i < n;++i) {
		b[i] = {a[i], a[(i + 1) % n]};
	}
	std::vector<std::pair<db, db>> ok, del;
	std::vector<db> o;
	for(auto [x, y] : b) {
		if(x.y > y.y) std::swap(x, y);
		if(x.y <= 0 && y.y > 0) {
			o.push_back((x.x * (0 - y.y) + y.x * (x.y - 0)) / (x.y - y.y));
		}
	}
	assert(o.size() % 2 == 0);
	sort(o.begin(), o.end());
	for(int i = 0;i < (int) o.size();i += 2) {
		ok.emplace_back(o[i], o[i + 1]);
	}
	for(auto [x, y] : b) {
		if(x.y > y.y) std::swap(x, y);
		if(x.y >= R) continue;
		if(y.y <= -R) continue;
		vec2 mid = {0, 0};
		if(x.y <= 0 && y.y > 0) {
			mid.x = (x.x * (0 - y.y) + y.x * (x.y - 0)) / (x.y - y.y);
		} else {
			mid.x = fabs(y.y) < fabs(x.y) ? y.x : x.x;
		}
		db le = mid.x, ri = mid.x, s = 1e7;
		auto chk = [&](db d) {
			return dist({x, y}, vec2{d, 0}) <= R + eps;
		};
		assert(chk(mid.x));
		for(int i = 0;i < 100;++i) {
			s /= 2;
			if(chk(le - s)) le -= s;
			if(chk(ri + s)) ri += s;
		}
		del.emplace_back(le, ri);
		o.push_back(le);
		o.push_back(ri);
	}
	sort(o.begin(), o.end());
	std::vector<int> cnt(o.size());
	for(auto [l, r] : ok) {
		int L = lower_bound(o.begin(), o.end(), l) - o.begin();
		int R = lower_bound(o.begin(), o.end(), r) - o.begin();
		cnt[L] += 1;
		cnt[R] -= 1;
	}

	for(auto [l, r] : del) {
		int L = lower_bound(o.begin(), o.end(), l) - o.begin();
		int R = lower_bound(o.begin(), o.end(), r) - o.begin();
		cnt[L] -= 1;
		cnt[R] += 1;
	}
	db ans = 0;
	for(int i = 0;i + 1 < (int) o.size();++i) {
		if(i) cnt[i] += cnt[i - 1];
		if(cnt[i] > 0) {
			ans += o[i + 1] - o[i];
		}
	}
	printf("%.10Lf\n", ans);
}