// 那就是希望。
// 即便需要取模，也是光明。

#include <algorithm>
#include <math.h>
#include <stdio.h>
#include <vector>
typedef long long llt;
typedef unsigned uint;typedef unsigned long long ullt;
typedef bool bol;typedef char chr;typedef void voi;
typedef double dbl;
template<typename T>bol _max(T&a,T b){return(a<b)?a=b,true:false;}
template<typename T>bol _min(T&a,T b){return(b<a)?a=b,true:false;}
template<typename T>T lowbit(T n){return n&-n;}
template<typename T>T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<typename T>T lcm(T a,T b){return(a!=0||b!=0)?a/gcd(a,b)*b:(T)0;}
template<typename T>T exgcd(T a,T b,T&x,T&y){if(b!=0){T ans=exgcd(b,a%b,y,x);y-=a/b*x;return ans;}else return y=0,x=1,a;}
template<typename T>T power(T base,T index,T mod)
{
    T ans=1%mod;
    while(index)
    {
        if(index&1)ans=ans*base%mod;
        base=base*base%mod,index>>=1;
    }
    return ans;
}
ullt S[5005],L[5005],R[5005],a;
dbl V[5005],T[5005];
int main()
{
#ifdef MYEE
    freopen("QAQ.in","r",stdin);
    // freopen("QAQ.out","w",stdout);
#else
#if !defined(ONLINE_JUDGE)
    freopen("b.in","r",stdin);
    freopen("b.out","w",stdout);
#endif
#endif
    uint n;scanf("%u%llu",&n,&a);
    for(uint i=0;i<=n;i++)scanf("%llu",S+i);
    for(uint i=0;i<=n;i++)scanf("%llu%llu",L+i,R+i);
    for(uint i=1;i<=n;i++)_max(L[i],L[i-1]);
    for(uint i=n;i;i--)_min(R[i-1],R[i]);
    for(uint i=0;i<=n;i++)if(L[i]>R[i])return puts("kaibai"),0;
    for(uint i=1;i<=n;i++){
        T[i]=1e18;
        for(uint l=0;l<i;l++){
            dbl s=S[i]-S[l],dt=L[i]-T[l];if(dt<0)dt=0;
            dbl v=V[l];
            if(dt*v+dt*dt/2*a<s)
                dt=(sqrt(v*v+2*a*s)-v)/a,v+=dt*a;
            else if(a/2*dt*dt<s)
                v=a*dt/2+s/dt;
            else
                v=sqrt(2*a*s);
            dbl t=T[l]+dt;
            _min(T[i],t);_max(V[i],v);
        }
        if(T[i]>R[i])return puts("kaibai"),0;
    }
    printf("%lf\n",T[n]);
    return 0;
}
// 那就是希望。
// 即便需要取模，也是光明。