#include <bits/stdc++.h>
#define x real()
#define y imag()
using namespace std;
const int Nmax = 210;
const long double eps = 1e-6;
typedef complex<long double> point;
long double dist[Nmax][2][Nmax][2];
int S, N;
point a[Nmax], O, W;
point S1[10], S2[10];
int Pair(int k)
{
if(k >= 2*N) return -1;
return k^1;
}
long double distanta(point A, point B)
{
return abs(A - B);
}
long double cross(point a, point b)
{
return (conj(a) * b).y;
}
long double dot(point a, point b)
{
return (conj(a) * b).x;
}
bool on_segm(point A, point B, point C) /// este A pe segmentul [BC]?
{
return distanta(A, B) + distanta(A, C) - distanta(B, C) < eps;
}
point reflect(point A, point B, point C)
{
A -= B; C -= B;
return B + (conj(A / C)) * C;
}
point perp(point A, point B, point C) /// perpendiculara din A pe dreapta BC
{
return (A + reflect(A, B, C)) / (long double) 2;
}
point intersect(point a, point b, point c, point d)
{
b -= a; c -= a; d -= a;
long double c1 = cross(c, b), c2 = cross(d, b);
return a + (c1 * d - c2 * c) / (c1 - c2);
}
bool inters_segm(point a, point b, point c, point d)
{
if(cross(c-a, b-a) == cross(d-a, b-a)) return 0; /// paralele
point P = intersect(a, b, c, d);
return on_segm(P, a, b) && on_segm(P, c, d);
}
bool pass(point a, point b)
{
return inters_segm(a, b, O, W);
}
bool is_ok(point A, point B) /// trece dreapta AB prin interiorul patratului initial?
{
int i;
for(i=0; i<4; ++i)
if(inters_segm(A, B, S1[i], S2[i])) return 0;
return 1;
}
void add_edge(int s, int t, long double D, bool p)
{
dist[s][0][t][p] = min(dist[s][0][t][p], D);
dist[s][1][t][p^1] = min(dist[s][1][t][p^1], D);
swap(s, t);
dist[s][0][t][p] = min(dist[s][0][t][p], D);
dist[s][1][t][p^1] = min(dist[s][1][t][p^1], D);
}
void find_edge(int s, int t)
{
if(Pair(s) == t) /// puncte de pe acelasi segment
{
add_edge(s, t, 0, pass(a[s], a[t]));
return;
}
if(is_ok(a[s], a[t]))
add_edge(s, t, distanta(a[s], a[t]), pass(a[s], a[t]));
int z = Pair(s);
if(z != -1)
{
point P = perp(a[t], a[s], a[z]);
if(on_segm(P, a[s], a[z]) && is_ok(a[t], P))
add_edge(s, t, distanta(a[t], P), pass(a[t], P) ^ pass(P, a[s]));
}
swap(s, t);
z = Pair(s);
if(z != -1)
{
point P = perp(a[t], a[s], a[z]);
if(on_segm(P, a[s], a[z]) && is_ok(a[t], P))
add_edge(s, t, distanta(a[t], P), pass(a[t], P) ^ pass(P, a[s]));
}
}
int main()
{
// freopen("input", "r", stdin);
cin.sync_with_stdio(false);
int i, n;
cin >> N >> S;
for(i=0; i<N; ++i)
{
long double X, Y;
cin >> X >> Y;
a[2*i] = {X, Y};
cin >> X >> Y;
a[2*i+1] = {X, Y};
}
n = 2*N;
a[n++] = {-S, S};
a[n++] = {S, S};
a[n++] = {S, -S};
a[n++] = {-S, -S};
O = {0, 0}; W = {251, 257};
S1[0] = S2[3] = a[2*N] + point(eps, -eps);
S1[1] = S2[0] = a[2*N+1] + point(-eps, -eps);
S1[2] = S2[1] = a[2*N+2] + point(-eps, +eps);
S1[3] = S2[2] = a[2*N+3] + point(eps, +eps);
int j, k, i2, j2, k2;
for(i=0; i<n; ++i)
for(i2=0; i2<2; ++i2)
{
for(j=0; j<n; ++j)
for(j2=0; j2<2; ++j2)
dist[i][i2][j][j2] = 10 * S;
dist[i][i2][i][i2] = 0;
}
for(i=0; i<n; ++i)
for(j=i+1; j<n; ++j)
find_edge(i, j);
for(k=0; k<n; ++k)
for(k2=0; k2<2; ++k2)
for(i=0; i<n; ++i)
for(i2=0; i2<2; ++i2)
for(j=0; j<n; ++j)
for(j2=0; j2<2; ++j2)
dist[i][i2][j][j2] = min(dist[i][i2][j][j2], dist[i][i2][k][k2] + dist[k][k2][j][j2]);
long double ans = 10 * S;
for(i=0; i<n; ++i)
{
ans = min(ans, dist[i][0][i][1]);
// assert(dist[i][0][i][1] == dist[i][1][i][0]);
}
cout << setprecision(10) << fixed;
cout << ans << '\n';
return 0;
}
