#include <bits/stdc++.h>
using namespace std;
const int MAXN = 222;
typedef pair<double, double> pi;
double ccw(pi a, pi b, pi c){
double dx1 = b.first - a.first;
double dy1 = b.second - a.second;
double dx2 = c.first - a.first;
double dy2 = c.second - a.second;
return dx1 * dy2 - dy1 * dx2;
}
double dot(pi a, pi b, pi c){
double dx1 = b.first - a.first;
double dy1 = b.second - a.second;
double dx2 = c.first - a.first;
double dy2 = c.second - a.second;
return dx1 * dx2 + dy1 * dy2;
}
double pdist(pi a, pi b){
return hypot(a.first - b.first, a.second - b.second);
}
const double eps = 1e-7;
bool line_segment_intersection(pi a, pi b, pi c, pi d){
double k1 = ccw(a, b, c);
double k2 = ccw(a, b, d);
if(k1 > eps && k2 > eps) return false;
if(k1 < -eps && k2 < -eps) return false;
k1 = ccw(c, d, a);
k2 = ccw(c, d, b);
if(k1 > eps && k2 > eps) return false;
if(k1 < -eps && k2 < -eps) return false;
return true;
}
int n, c;
pi a[MAXN];
struct node{
int pos, arg;
double dist;
bool operator<(const node &n)const{
return dist > n.dist;
}
};
struct seg{
double first;
int second, basecross;
};
vector<seg> gph[MAXN];
double dist[2][MAXN];
bool vis[2][MAXN];
double solve(int p){
priority_queue<node> pq;
for(int i=0; i<2; i++){
for(int j=0; j<2*n+8; j++){
dist[i][j] = 1e9;
vis[i][j] = 0;
}
}
dist[0][p] = 0;
while(true){
int sx = -1, sy = -1;
double cur = 1e9;
for(int i=0; i<2; i++){
for(int j=0; j<2*n+8; j++){
if(!vis[i][j] && dist[i][j] < cur){
cur = dist[i][j];
sx = i;
sy = j;
}
}
}
if(sx == -1 || sy == -1) break;
vis[sx][sy] = 1;
for(auto &i : gph[sy]){
if(dist[sx ^ i.basecross][i.second] > i.first + cur){
dist[sx ^ i.basecross][i.second] = i.first + cur;
}
}
}
return dist[1][p];
}
bool is_cross(pi a, pi b){
return line_segment_intersection(a, b, pi(0, 0), pi(233, 569));
}
void makeGraph(){
auto add_edge = [&](int s, int e, double x, bool augment = false){
// printf("%d %d %.10f\n",s ,e , x);
gph[s].push_back({x, e, is_cross(a[s], a[e]) ^ augment});
gph[e].push_back({x, s, is_cross(a[s], a[e]) ^ augment});
};
for(int i=0; i<n+4; i++){
add_edge(2*i, 2*i+1, 0);
}
add_edge(2*n, 2*n+2, 2*c);
add_edge(2*n, 2*n+4, 2*c);
add_edge(2*n+2, 2*n+6, 2*c);
add_edge(2*n+4, 2*n+6, 2*c);
for(int i=0; i<2*n+8; i++){
for(int j=0; j<2*n; j++){
if(j % 2 == 1) continue;
if(i / 2 == j / 2) continue;
pi p1 = a[i];
pi p2 = pi(-1, -1);
if(dot(a[j], a[j+1], p1) < 0 || dot(a[j+1], a[j], p1) < 0){
if(pdist(a[j], p1) < pdist(a[j+1], p1)) p2 = a[j];
else p2 = a[j+1];
}
else{
double arg = ccw(a[j], a[j+1], p1) / pdist(a[j], a[j+1]);
double dx = (a[j+1].first - a[j].first) / pdist(a[j], a[j+1]);
double dy = (a[j+1].second - a[j].second) / pdist(a[j], a[j+1]);
p2 = p1;
p2.first += dy * arg;
p2.second -= dx * arg;
}
if(i == 2 * n || i == 2 * n + 1){
if(p2.first <= -c || p2.second <= -c) {
add_edge(i, j, pdist(p1, p2), is_cross(a[i], a[j]) ^ is_cross(p1, p2) ^ is_cross(p2, a[j]));
}
else continue;
}
if(i == 2 * n + 2 || i == 2 * n + 3){
if(p2.first <= -c || p2.second >= c){
add_edge(i, j, pdist(p1, p2), is_cross(a[i], a[j]) ^ is_cross(p1, p2) ^ is_cross(p2, a[j]));
}
else continue;
}
if(i == 2 * n + 4 || i == 2 * n + 5){
if(p2.first >= c || p2.second <= -c){
add_edge(i, j, pdist(p1, p2), is_cross(a[i], a[j]) ^ is_cross(p1, p2) ^ is_cross(p2, a[j]));
}
else continue;
}
if(i == 2 * n + 6 || i == 2 * n + 7){
if(p2.first >= c || p2.second >= c){
add_edge(i, j, pdist(p1, p2), is_cross(a[i], a[j]) ^ is_cross(p1, p2) ^ is_cross(p2, a[j]));
}
else continue;
}
double lx = -c, rx = c;
if(line_segment_intersection(p1, p2, pi(lx, rx), pi(lx, lx))) continue;
if(line_segment_intersection(p1, p2, pi(lx, rx), pi(rx, rx))) continue;
if(line_segment_intersection(p1, p2, pi(rx, rx), pi(rx, lx))) continue;
if(line_segment_intersection(p1, p2, pi(rx, lx), pi(lx, lx))) continue;
add_edge(i, j, pdist(p1, p2), is_cross(a[i], a[j]) ^ is_cross(p1, p2) ^ is_cross(p2, a[j]));
}
}
}
int main(){
cin >> n >> c;
for(int i=0; i<2*n; i++){
cin >> a[i].first >> a[i].second;
}
a[2*n+0] = a[2*n+1] = pi(-c, -c);
a[2*n+2] = a[2*n+3] = pi(-c, c);
a[2*n+4] = a[2*n+5] = pi(c, -c);
a[2*n+6] = a[2*n+7] = pi(c, c);
makeGraph();
double ans = 1e9;
for(int i=0; i<2*n+8; i++) ans = min(ans, solve(i));
printf("%.10f\n", ans);
}
