#include<bits/stdc++.h>
#define fi first
#define se second
#define mk(x,y) make_pair(x,y)
using namespace std;
typedef long double D;
const D eps=1e-9,INF=4e9;
const int N=5005;
int n,A,s[N],l[N],r[N];
D f[N];
void upd(pair<D,D>&x,pair<D,D>y){x.fi=max(x.fi,y.fi),x.se=min(x.se,y.se);}
bool chk(pair<D,D>x,D y){return x.fi-eps<=y&&y<=x.se+eps;}
D solve(D a,D b,D c){return (-b+sqrt(b*b-4*a*c))/(2*a);}
int main(){
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(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];
	r[1]=0;
	f[1]=0;
	for (int i=2;i<=n+1;++i)f[i]=-INF;
	D ans=INF*2;
	for (int i=1;i<=n;++i){
		if (f[i]<-eps)continue;
		auto V=mk((D)0.0,(D)f[i]),T=mk((D)0.0,(D)INF);
		for (int j=i+1;j<=n;++j){
			D v0=(s[j]-s[i])*1.0/(r[j]-r[i])-0.5*A*(r[j]-r[i]),v1=(s[j]-s[i])*1.0/max(eps,(D)l[j]*1.0-r[i])-0.5*A*max(eps,(D)l[j]*1.0-r[i]);
			if (chk(V,v0))f[j]=max(f[j],v0+1.0*A*(r[j]-r[i]));
			D tt=sqrt(2.0*(s[j]-s[i])/A);
			D t0=r[j]-r[i]-tt,t1=max(eps,l[j]-r[i]-tt);
			if (chk(T,t0))f[j]=max(f[j],tt*A);
			if (r[j]<r[i])v0=INF,v1=0;
			upd(V,mk(v0,v1));
			upd(T,mk(t1,t0));
			if (V.fi>V.se&&T.fi>T.se)break;
		} 
		if (V.fi<V.se)ans=min(ans,r[i]+solve(0.5*A,V.se,-(s[n+1]-s[i])));
		if (T.fi<T.se)ans=min(ans,r[i]+T.fi+sqrt((s[n+1]-s[i])*2.0/A));
	}
	if (ans>r[n+1]||abs(ans-INF)<eps)cout<<"kaibai";
	else cout<<fixed<< setprecision(6)<<max(ans,(D)l[n+1]*1.0);
}