#include<bits/stdc++.h>
#define ld long double
#define ci const int 
#define ll long long
#define fo(i,l,r) for(int i=(l);i<=(r);++i)
#define fu(i,l,r) for(int i=(l);i<(r);++i)
#define fd(i,l,r) for(int i=(l);i>=(r);--i)
#define P(x) __builtin_popcount(x)
#define gcd(x,y) __gcd(x,y)
using namespace std;
ci mod=1e9+7,N=1e6+5;
const ld eps=1e-9;
mt19937 rad(chrono::steady_clock::now().time_since_epoch().count());
inline ll read(){ll u=0,f=1;char o;while((o=getchar())<48||o>57)if(o=='-')f=-1;u=(o^48);while((o=getchar())>=48&&o<=57)u=(u<<1)+(u<<3)+(o^48);return u*f;}
void write(ll x){if(x<0)putchar('-'),x=-x;if(x>9)write(x/10);putchar(x%10+48);}
bool ST;
ll n,s[N];
ld a,len,v,t,L[N],R[N];
ld check(ld v)
{
	return (-v+sqrt(v*v+2*a*len))/a;
}
bool ED;
signed main()
{//cerr<<(&ST-&ED)/1048576.0<<'\n';
//	freopen("1.in","r",stdin);
//	freopen("1.out","w",stdout);
//	freopen("accel.in","r",stdin);
//	freopen("accel.out","w",stdout);
	n=read();a=read();
	fo(i,1,n+1)
	{
		s[i]=read();
	}
	fo(i,1,n+1)
	{
		L[i]=read(),R[i]=read();
	}
	ld t=0;
	fo(i,2,n+1)
	{
		len=s[i];
		t=max(t,L[i]-check(0));
	}
	printf("%.10Lf",t+check(0)),cout<<'\n';
}