#include<bits/stdc++.h>
#define N 5010
#define LL long long
#define ULL unsigned long long
#define DB double
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define per(i,a,b) for(int i=a;i>=b;i--)
#define INF 1e13
#define pir pair<int,int>
#define mp(i,j) make_pair(i,j)
#define fi first
#define se second
using namespace std;
template <typename T> inline void read(T &a)
{
	a=0;T w=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){a=(a<<3)+(a<<1)+(ch^48);ch=getchar();}
	a*=w;
}
template <typename T,typename ...Args> inline
void read(T &x,Args &...args){read(x);read(args...);}
int n,a,s[N],l[N],r[N];
DB f[N],ans=INF;
inline DB solve_v(DB x,DB t){if(t<0) return INF;return 1.0*(x-0.5*a*t*t)/t;}
inline DB solve_t(DB x,DB v0){return (-2*v0+sqrt(4.0*v0*v0+8.0*a*x))/(2.0*a);}
signed main()
{
	read(n,a);
	rep(i,1,n+1) read(s[i]);
	rep(i,1,n+1) read(l[i],r[i]);
	rep(i,1,n+1) l[i]=max(l[i-1],l[i]);
	per(i,n,1) r[i]=min(r[i+1],r[i]);
	rep(i,1,n+1) if(l[i]>r[i]) return printf("kaibai\n"),0;
	f[0]=l[1]=r[1]=0;rep(i,2,n+1) f[i]=-1;
	
	
//	rep(i,1,n+1) printf("%d ",l[i]);printf("\n");
//	rep(i,1,n+1) printf("%d ",r[i]);printf("\n");
	
	rep(i,1,n) if(f[i]>=0)
	{
//		printf("begin %d ===================================\n",i);
		DB L=0,R=f[i];
		rep(j,i+1,n+1)
		{
			DB dis=s[j]-s[i],Lv=solve_v(dis,r[j]-r[i]),Rv=solve_v(dis,l[j]-r[i]);//最低要求速度，最高允许速度 
			L=max(L,Lv);R=min(R,Rv);if(L>R) break;
//			printf("to %d for v L=%.3lf R=%.3lf\n",j,L,R);
			f[j]=max(f[j],Lv+(r[j]-r[i])*a);//用最长的时间加速
			if(j==n+1) ans=min(ans,r[i]+solve_t(s[n+1]-s[i],R));//直接到终点 
		}
		L=0,R=r[i+1]-r[i];
		rep(j,i+1,n+1)
		{
			DB dis=s[j]-s[i],t=sqrt(2*dis/a);
			DB Lt=l[i+1]-r[i]-t,Rt=r[i+1]-r[i]-t;//最低等待时间，最高等待时间 
			L=max(L,Lt);R=min(R,Rt);if(L>R) break;
//			printf("dis=%.3lf t=%.3lf\n",dis,t);
//			printf("to %d for t L=%.3lf R=%.3lf\n",j,L,R);
			f[j]=max(f[j],a*t);
			if(j==n+1) ans=min(ans,r[i]+L+t);//直接到终点 
		}
	}
	if(ans>=INF-10) return printf("kaibai\n"),0;
	printf("%.5lf\n",ans);
	return 0;
}