#include <bits/stdc++.h>

using namespace std;

using i64=long long;
using db=double;
using vi=vector<int>;
using pii=pair<int,int>;

template<typename T>
inline T read(){
    T x=0,f=0;char ch=getchar();
    while(!isdigit(ch)) f|=(ch=='-'),ch=getchar();
    while(isdigit(ch)) x=(x*10)+(ch^48),ch=getchar();
    return !f?x:-x;
}

#define rdi read<int>
#define rdi64 read<i64>
#define fi first
#define se second
#define mp make_pair
#define pb push_back

const int N=5010;
const db eps=1e-7;

int n,a,s[N];
int L[N],R[N];

db f[N];

db calc_v(db s,db t,db a) {return (2*s-a*t*t)/(2*t);}
db calc_t(db s,db v0,db a) {return (sqrt(v0*v0+2*s*a)-v0)/a;}

// 最大初速度  最小等待时间
db vmx[N][N],   tmi[N][N];
// 最小初速度  最大等待时间
db vmi[N][N],  tmx[N][N];
void init(){
    for(int i=0;i<=n;i++){
        for(int j=i+1;j<=n;j++){
            if(L[i]>=L[j]){
                vmx[i][j]=1e18;
                tmi[i][j]=-1e18;
            }
            else{
                vmx[i][j]=calc_v(s[j]-s[i],L[j]-L[i],a);
                tmi[i][j]=(L[j]-L[i])-calc_t(s[j]-s[i],0,a);
                if(tmi[i][j]<-eps) tmi[i][j]=-1e18;
            }

            if(L[i]>=R[j]){
                puts("kaibai");
                exit(0);
            }
            else{
                vmi[i][j]=calc_v(s[j]-s[i],R[j]-L[i],a);
                tmx[i][j]=(R[j]-L[i])-calc_t(s[j]-s[i],0,a);
                if(tmx[i][j]<-eps) tmx[i][j]=-1e18;
            }
        }
    }
}

int main(){
#ifdef LOCAL
    freopen("1.in","r",stdin);
    freopen("1.out","w",stdout);
#endif
    n=rdi(),a=rdi();
    for(int i=0;i<=n;i++) s[i]=rdi();
    for(int i=0;i<=n;i++) L[i]=rdi(),R[i]=rdi();
    init();

    db ans=1e18;
    for(int i=1;i<=n;i++) f[i]=-1e18;
    f[0]=0;
    for(int i=0;i<=n;i++){
        db v0l=0,v0r=f[i];
        db t0l=0,t0r=1e18;
        for(int j=i+1;j<=n;j++){
            v0l=max(v0l,vmi[i][j]),v0r=min(v0r,vmx[i][j]);
            t0l=max(t0l,tmi[i][j]),t0r=min(t0r,tmx[i][j]);
            if(v0l<=v0r&&v0r<=f[i]&&fabs(v0r-vmx[i][j])<eps)
                f[j]=max(f[j],v0r+(db)(L[j]-L[i])*a);
            if(t0l<=t0r&&fabs(t0l-tmi[i][j])<eps)
                f[j]=max(f[j],(L[j]-L[i]-t0l)*a);
        }
        if(i<n){
            if(v0l<=v0r)
                ans=min(ans,L[i]+calc_t(s[n]-s[i],v0r,a));
            if(t0l<=t0r)
                ans=min(ans,L[i]+t0l+calc_t(s[n]-s[i],0,a));
        }
    }
    if(f[n]>=0) ans=L[n];
    if(ans>1e9) puts("kaibai");
    else printf("%.7lf\n",ans);
    return 0;
}