# include <bits/stdc++.h>
using namespace std;
constexpr double INF=1e9;
int S,id[110][2];
double f[210][210];
struct Point
{
	double x,y;
	Point(){}
	Point(double x,double y):x(x),y(y){}
	Point operator+(const Point &t)const{return Point(x+t.x,y+t.y);}
	Point operator-(const Point &t)const{return Point(x-t.x,y-t.y);}
	Point operator*(const double &t)const{return Point(x*t,y*t);}
	double operator*(const Point &t)const{return x*t.x+y*t.y;}
	Point operator/(const double &t)const{return Point(x/t,y/t);}
};
struct Seg
{
	Point A,B;
	Seg(){}
	Seg(const Point &A,const Point &B):A(A),B(B){}
}a[110];
inline double Abs(const Point &t){return sqrt(t.x*t.x+t.y*t.y);}
inline void chkmin(double &x,const double &y){x=min(x,y);}
inline bool contain(const Point &A,const Point &B,const Point &C)
{
	return C.x>=min(A.x,B.x) && C.x<=max(A.x,B.x) && C.y>=min(A.y,B.y) && C.y<=max(A.y,B.y);
}
inline Point geth(const Point &A,const Point &B,const Point &C)
{
	auto D=(B-A)/Abs(B-A);
	return A+D*((C-A)*D);
}
inline bool calc(const Point &A,const Point &B){return min(A.x,B.x)<0 && max(A.x,B.x)>=0 && min(A.y,B.y)>0;}
bool chk(const Point &A,const Point &B)
{
	if((abs(A.x)<S && abs(A.y)<S) || (abs(B.x)<S && abs(B.y)<S)) return false;
	if(A.x-A.y!=B.x-B.y)
	{
		double a=A.x*B.y-B.x*A.y,b=(B.y-B.x)-(A.y-A.x);
		if(b<0) a=-a,b=-b;
		if(a>=b*max(min(A.x,B.x),min(A.y,B.y)) && a<=b*min(max(A.x,B.x),max(A.y,B.y)) && abs(a)<b*S) return false;
	}
	if(A.x+A.y!=B.x+B.y)
	{
		double a=A.x*B.y-B.x*A.y,b=(B.x+B.y)-(A.x+A.y);
		if(b<0) a=-a,b=-b;
		if(a>=b*max(min(A.x,B.x),-max(A.y,B.y)) && a<=b*min(max(A.x,B.x),-min(A.y,B.y)) && abs(a)<b*S) return false;
	}
	return true;
}
pair<double,double> Dis(int i,int j)
{
	double ans[2]={INF,INF};
	for(auto P:{a[i].A,a[i].B})
		for(auto Q:{a[j].A,a[j].B})
			if(chk(P,Q))
				chkmin(ans[calc(a[i].A,P)^calc(P,Q)^calc(Q,a[j].A)],Abs(P-Q));
	for(auto P:{a[i].A,a[i].B})
	{
		auto Q=geth(a[j].A,a[j].B,P);
		if(contain(a[j].A,a[j].B,Q) && chk(P,Q))
			chkmin(ans[calc(a[i].A,P)^calc(P,Q)^calc(Q,a[j].A)],Abs(P-Q));
	}
	for(auto P:{a[j].A,a[j].B})
	{
		auto Q=geth(a[i].A,a[i].B,P);
		if(contain(a[i].A,a[i].B,Q) && chk(P,Q))
			chkmin(ans[calc(a[i].A,Q)^calc(Q,P)^calc(P,a[j].A)],Abs(P-Q));
	}
	return {ans[0],ans[1]};
}
int main()
{
	int n,tot=0;
	double ans=INF;
	cin>>n>>S;
	for(int i=1;i<=n;i++) scanf("%lf%lf%lf%lf",&a[i].A.x,&a[i].A.y,&a[i].B.x,&a[i].B.y);
	for(int x:{S,-S})
		for(int y:{S,-S})
			a[++n]=Seg(Point(x,y),Point(x,y));
	for(int i=1;i<=n;i++) id[i][0]=++tot,id[i][1]=++tot;
	for(int i=1;i<=n;i++) f[id[i][0]][id[i][1]]=f[id[i][1]][id[i][0]]=INF;
	for(int i=1;i<=n;i++)
		for(int j=1;j<i;j++)
		{
			double dis[2];
			tie(dis[0],dis[1])=Dis(i,j);
			for(int k:{0,1})
			{
				f[id[i][k]][id[j][k]]=f[id[j][k]][id[i][k]]=dis[0];
				f[id[i][k]][id[j][k^1]]=f[id[j][k]][id[i][k^1]]=dis[1];
			}
		}
	for(int k=1;k<=tot;k++)
		for(int i=1;i<=tot;i++)
			for(int j=1;j<=tot;j++)
				chkmin(f[i][j],f[i][k]+f[k][j]);
	for(int i=1;i<=n;i++) chkmin(ans,f[id[i][0]][id[i][1]]);
	printf("%.4lf\n",ans);
	return 0;
}