#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 long 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] + 1e-6) return puts("kaibai"),0;
		else if(c + t + 1e-6 >= l[i]) v = nv,c += t;
		else
		{
			if(v * (l[i] - c) <= S + 1e-6) v = a * t + S / t - 0.5 * a * t;
			else if(0.5 * a * (l[i] - c) * (l[i] - c) + 1e-6 >= S) v = sqrt(2 * a * S);
			else v = sqrt(2 * a * S) + S / (l[i] - c) - 0.5 * a * (l[i] - c);
			c = l[i];
		}
	}
	printf("%Lf",c);
	return 0;
}