#include <bits/stdc++.h>
using namespace std;
const int N=5005;
typedef long double ldb;
const ldb Inf=1e18,der=1e-10;
int n,a;
int s[N],l[N],r[N];
ldb dp[N],ans;
ldb cal(ldb x,ldb y)
{
	ldb der=sqrt(4*x*x+8*y*a);
	der-=2*x;
	der/=2*a;
	return der; 
}
void sol_v(int t)
{
	int i,j;
	ldb vl=0,vr=dp[t],nvl,nvr,tl,tr,ss;
//	cout<<t<<endl;
	for(i=t+1;i<=n;i++)
	{
		ss=s[i]-s[t];
		tl=l[i]-r[t],tr=r[i]-r[t];
	//	cout<<tl<<" "<<tr<<endl;
		//	if(tr<der) return;
		nvl=(ss-0.5*a*tr*tr)/tr;
	//	cout<<t<<" "<<i<<" "<<nvl<<endl;
		vl=max(vl,nvl);
	//	cout<<"ss "<<(ss-0.5*a*tl*tl)/tl<<endl;
		if(tl>0) vr=min(vr,(ss-0.5*a*tl*tl)/tl);
		if(vr<vl-der) return;//cout<<vl<<" "<<vr<<endl;
		if(vl-der<nvl) dp[i]=max(dp[i],nvl+(ldb)tr*a);//,cout<<"ukcdoco "<<i<<" "<<nvl+(ldb)tr*a<<endl;
		if(i==n) ans=min(ans,r[t]+cal(vr,s[n]-s[t]));
	}
//	if(i==n+1) ans=min(ans,cal(t));
}
void sol_t(int t)
{
	int i,j;
	ldb lt=0,rt=r[t+1]-r[t],ntl,ntr,ss;//,tt;
//	cout<<rt<<endl;
	for(i=t+1;i<=n;i++)
	{
		ss=s[i]-s[t];
		ntl=sqrt(2*ss/(1.0*a));
		lt=max(lt,l[i]-r[t]-ntl);
	//	tt=rt;
		rt=min(rt,r[i]-r[t]-ntl);
	//	cout<<ntl<<" "<<lt<<" "<<rt<<endl;
		if(rt<lt) return;
	//	cout<<tt<<endl;
		if(rt>=(r[i]-r[t]-ntl)) dp[i]=max(dp[i],(ldb)ntl*a);//,cout<<"qwert "<<i<<" "<<ntl*a<<endl;
	//	tt=rt;
		if(i==n) ans=min(ans,r[t]+lt+ntl);
	}
//	if(i==n+1) ans=min(ans,dp[t]+lt+ntl);
}
int main()
{
	scanf("%d%d",&n,&a);
	int i,j;
	for(i=0;i<=n;i++) scanf("%d",&s[i]);
	for(i=0;i<=n;i++) scanf("%d%d",&l[i],&r[i]);
	for(i=1;i<=n;i++) l[i]=max(l[i],l[i-1]);
	r[n+1]=0x3f3f3f3f;
	for(i=n;i>=0;--i)
	{
		r[i]=min(r[i],r[i+1]);
	//	cout<<i<<" "<<r[i]<<endl;
		if(l[i]>r[i])
		{
			puts("kaibai");
			return 0;
		}
	}
	l[0]=r[0]=0;
	ans=Inf;
	for(i=1;i<=n;i++) dp[i]=-Inf; 
	dp[0]=0;
	for(i=0;i<n;i++)
	{
		if(dp[i]==-Inf) continue;
		sol_v(i);
		sol_t(i);
	//	for(j=1;j<=n;j++) cout<<dp[j]<<" ";
	//	puts("");
	} 
	if(ans>10000000) puts("kaibai");
	else printf("%.10Lf",ans);
	return 0;
}