#include<cstdio>
#include<cmath>
#define fo(i,x,y) for(int i = x;i <= y;++i)
#define fd(i,x,y) for(int i = x;i >= y;--i)
#define _is 1048576
#define gc() ib[++bi]
#define D double
using namespace std;
char ib[_is];int bi = -1;
int rd()
{
	int x = 0;char ch = gc();
	while(ch < 48 || ch > 57) ch = gc();
	while(ch >= 48 && ch <= 57) x = x * 10 + ch - 48,ch = gc();return x;
}
int n,a,s[5010],l[5010],r[5010];
void Mi(int &x,int y) {if(y < x) x = y;}
void Mx(int &x,int y) {if(y > x) x = y;}
int main()
{
	fread(ib,1,_is,stdin);
    n = rd(),a = rd();
    fo(i,0,n) s[i] = rd();
    fo(i,0,n) l[i] = rd(),r[i] = rd();
    fo(i,2,n) Mx(l[i],l[i - 1]);
    fd(i,n - 1,1) Mi(r[i],r[i + 1]);
    fo(i,1,n) if(l[i] > r[i]) return puts("kaibai"),0;
    D v = 0,c = 0;
    fo(i,1,n)
    {
        D S = s[i] - s[i - 1];
        D nv = sqrt(2 * a * S + v * v),t = (nv - v) / a;
        if(c + t > r[i]) return puts("kaibai"),0;
        else if(c + t >= l[i]) v = nv,c += t;
        else
        {
            D t = l[i] - c,A = min(D(a),2 * S / t / t);
            c = l[i],v = S / t + A * t * 0.5;
            //0<=v'<=v,0<=a'<=a,max(v'+a't)
            //a'<=2S/(t^2)
            //max(S/t+a't/2)
        }
    }
    printf("%lf",c);
	return 0;
}