#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read()
{
	int aa=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9') {if(ch=='-') f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9')aa=(aa<<3)+(aa<<1)+ch-'0',ch=getchar();
	return aa*f;
}
const int M=5e3+10;
int n,a;
int s[M],l[M],r[M];
double f[M],ans=1e18;
main(){
	n=read();a=read();for(int i=1;i<=n+1;i++) s[i]=read();for(int i=1;i<=n+1;i++) l[i]=read(),r[i]=read();r[1]=0;
	for(int i=1;i<=n;i++){
		double l1=0,l2=0,r1=1e18,r2=f[i];
		//路径需要等待时间/提供等待时间 
		//路径速度限制 
		for(int j=i+1;j<=n;j++){
			//无初速度 
			if(r[j]<r[i]) break;double t=sqrt(2.0*(s[j]-s[i])*1.0/(1.0*a)),wt=r[j]-r[i]-t;//等待时间
			if(wt>=l1&&wt<=r1) f[j]=max(f[j],t*1.0*a);if(l[j]>r[i]) l1=max(l1,l[j]-r[i]-t);r1=min(r1,wt);
		    //有初速度
			double v0=(s[j]-s[i])*1.0/(1.0*(r[j]-r[i]))-0.5*a*((r[j]-r[i])*1.0);
			if(v0>=l2&&v0<=r2) f[j]=max(f[j],sqrt(2.0*a*(1.0*(s[j]-s[i]))+v0*v0)); 
		    if(l[j]>r[i]) r2=min(r2,(s[j]-s[i])*1.0/(1.0*(l[j]-r[i]))-0.5*a*(1.0*(l[j]-r[i])));l2=max(l2,v0);
		    if(j==n){
		    	if(l1<=r1&&sqrt(2.0*(s[n+1]-s[i])*1.0/(1.0*a))+l1+r[i]<=r[n+1]) ans=min(ans,sqrt(2.0*(s[n+1]-s[i])*1.0/(1.0*a))+l1+r[i]);
			    if(l2<=r2){double vmax=sqrt((s[n+1]-s[i])*1.0*a*2.0+r2*r2);ans=min(ans,(vmax-r2)*1.0/(1.0*a)+r[i]);}
			}
		}
	}
	if(ans==1e18) cout<<"kaibai";
	else printf("%0.6lf",ans);
}