#include<bits/stdc++.h>
#define db __float128
#define N 100005
#define rep(i,x,y) for(int i=x,i##end=y;i<=i##end;++i)
const db eps=1e-10;
inline db _reps(){return rand()/(db)RAND_MAX;}
inline db reps(){int ty=rand()&1?1:-1; return _reps()*eps*ty;}
inline int eq(const db&p){return p<-eps?-1:p>eps;}
inline int eq(const db&x,const db&y){return eq(x-y);}
struct point{
	db x,y;
	inline point operator+(const point&p)const{return point{x+p.x,y+p.y};}
	inline point operator-(const point&p)const{return point{x-p.x,y-p.y};}
	inline point operator*(const db&p)const{return point{x*p,y*p};}
	inline point operator/(const db&p)const{return point{x/p,y/p};}
	// multiply cross
	inline db operator^(const point&p)const{return x*p.y-y*p.x;}
	// point multiply
	inline db operator&(const point&p)const{return x*p.x+y*p.y;}
	inline db norm2(){return x*x+y*y;}
	inline db norm(){return sqrt(norm2());}
	inline void inv(){std::swap(x,y); x=-x;}
} rec[4];
int n,cnt;
bool vis[2005][2005];
struct vector{
	db x,y,z;
	inline vector operator+(const vector&p)const{return vector{x+p.x,y+p.y,z+p.z};}
	inline vector operator-(const vector&p)const{return vector{x-p.x,y-p.y,z-p.z};}
	inline vector operator^(const vector&p)const{return vector{y*p.z-z*p.y,z*p.x-x*p.z,x*p.y-y*p.x};}
	inline db operator&(const vector&p)const{return x*p.x+y*p.y+z*p.z;}
	inline void rnd(){x+=reps(),y+=reps(),z+=reps();}
} poi[N];

inline point intersection(point a1,point a2,point b1,point b2){
	point a=a2-a1,b=b2-b1,c=b1-a1;
	return a1+(a*((b^c)/(b^a)));
}

struct plane{
	int id[3];
	inline plane(int x=0,int y=0,int z=0){id[0]=x,id[1]=y,id[2]=z;}
	inline vector norm(){return (poi[id[1]]-poi[id[0]])^(poi[id[2]]-poi[id[0]]);}
} f[N],cpy[N];

inline bool isplane(plane x,vector y){return ((y-poi[x.id[0]])&x.norm())>0;}
inline db angle(point x,point y){return atan2(x^y,x&y);}
inline db calc(point x,point y,db r){
	point p=(x-y)/(x-y).norm();
	point q=p; p.inv();
	point mid=intersection(x,y,point{0,0},p);
	if(mid.norm()>r) return r*r*angle(x,y)/2;
	db d=sqrt(r*r-mid.norm2());
	point w1=mid+(q*d),w2=mid-(q*d);
	int b1=eq(x.norm2(),r*r)==1,b2=eq(y.norm2(),r*r)==1;
	if(b1&&b2){
		if(eq((x-w1)&(y-w1))<=0)
			return r*r*(angle(x,w1)+angle(w2,y))/2+(w1^w2)/2;
		return r*r*angle(x,y)/2;
	}
	if(b1) return (r*r*angle(x,w1)+(w1^y))/2;
	if(b2) return (r*r*angle(w2,y)+(x^w2))/2;
	return (x^y)/2;
}
inline db merge(point o,db r){
	db ret=0;
	rep(i,0,3) ret+=calc(rec[i]-o,rec[i+1&3]-o,r);
	return ret;
}
void convex_hull(){
	f[++cnt]=plane(1,2,3),f[++cnt]=plane(3,2,1);
	rep(i,4,n){
		int num=0;
		rep(j,1,cnt){
			int ty=isplane(f[j],poi[i]);
			if(!ty) cpy[++num]=f[j];
			rep(k,0,2) vis[f[j].id[k]][f[j].id[(k+1)%3]]=ty;
		}
		rep(j,1,cnt){
			rep(k,0,2){
				int x=f[j].id[k],y=f[j].id[(k+1)%3];
				if(vis[x][y]&&!vis[y][x]) cpy[++num]=plane(x,y,i);
			}
		}
		rep(j,1,num) f[j]=cpy[j]; cnt=num,num=0;
	}
}
int main(){
	srand(time(NULL));
	std::cin>>n;
	double stx,sty,edx,edy;
	std::cin>>stx>>sty>>edx>>edy;
	rec[0]={stx,sty},rec[1]={edx,sty},rec[2]={edx,edy},rec[3]={stx,edy};
	db area=0,ret=0;
	area=(edx-stx)*(edy-sty);
	rep(i,1,n){
		double x,y; std::cin>>x>>y;
		poi[i]=vector{x,y,x*x+y*y};
		poi[i].rnd();
	}
	convex_hull();
	rep(i,1,cnt){
		vector center=f[i].norm();
		point from1,to1,from2,to2,st,ed,a,b;
		st=point{poi[f[i].id[0]].x,poi[f[i].id[0]].y},ed=point{poi[f[i].id[1]].x,poi[f[i].id[1]].y};
		a=(st+ed)/2,b=ed-st,b.inv();
		from1=a,to1=b+a;
		st=point{poi[f[i].id[1]].x,poi[f[i].id[1]].y},ed=point{poi[f[i].id[2]].x,poi[f[i].id[2]].y};
		a=(st+ed)/2,b=ed-st,b.inv();
		from2=a,to2=b+a;
		point inter=intersection(from1,to1,from2,to2);
		db dis=(inter-point{poi[f[i].id[0]].x,poi[f[i].id[0]].y}).norm();
		if(center.z>0) ret+=area-merge(inter,dis);
		else ret+=merge(inter,dis);
	}
	printf("%.15lf\n",(double)(ret/area)+2);
	return 0;
}