#include<bits/stdc++.h>
#define ld long double
#define eps 1e-6
using namespace std;
int n;ld f[5005],a,s[5005],l[5005],r[5005],ans=1e9;
int main()
{
	cin.tie(0)->sync_with_stdio(0);
	cin>>n>>a;
	for(int i=1;i<=n+1;i++)cin>>s[i];
	for(int i=1;i<=n+1;i++)cin>>l[i]>>r[i];
	for(int i=2;i<=n;i++)f[i]=-1;f[1]=0;l[1]=r[1]=0;
	for(int i=1;i<=n;i++)
	{
		if(f[i]==-1)continue;
		ld lt=0,rt=1e9,lv=0,rv=f[i];
		for(int j=i+1;j<=n;j++)
		{
			if(lt>rt&&lv>rv)break;
			ld t=r[j]-r[i]+eps,x=s[j]-s[i];
			ld v=x/t-0.5*a*t;
			if(lv<=v&&v<=rv)f[j]=max(f[j],v+a*t);
			ld t2=r[j]-r[i]-sqrt(2*x/a);
			if(lt<=t2&&t2<=rt)f[j]=max(f[j],sqrt(2.0*a*x));
			lt=max(lt,l[j]-r[i]-sqrt(2.0*x/a));rt=min(rt,r[j]-r[i]-sqrt(2.0*x/a));
			ld Lt=max((ld)0.0,l[j]-r[i])+eps,Rt=r[j]-r[i]+eps,lv2=0,rv2=0;
			if(Rt<0)lv2=0,rv2=-1;
			else rv2=x/Lt-0.5*a*Lt,lv2=x/Rt-0.5*a*Rt;
			lv=max(lv,lv2);rv=min(rv,rv2);
		}
		if(lv<=rv)
		{
			ld t=-rv+sqrt(rv*rv+2.0*a*(s[n+1]-s[i]))/a;
			ans=min(ans,t+r[i]);
		}
		if(lt<=rt)
		{
			ld t=lt+sqrt(2.0*(s[n+1]-s[i])/a);
			ans=min(ans,t+r[i]);
		}
	}
	if(ans>r[n+1])cout<<-1;
	else cout<<fixed<<setprecision(6)<<max(ans,l[n+1]); 
	return 0;
}