#include<bits/stdc++.h>

 #define maxn 100010

 #define eps 1e-10

 using namespace std;

 double ans,S1,S2;

 struct P{

     double x,y;

     P(double a=,double b=){x=a,y=b;}

 };

 struct L{

     P a,b;

     double ang;

 };

 int sgn(double x){

     return (x>eps)-(x<-eps);

 }

 P operator - (P a,P b){

     return P(a.x-b.x,a.y-b.y);

 }

 double operator * (P a,P b){

     return a.x*b.y-a.y*b.x;

 }

 bool operator < (L a,L b){

     if(sgn(a.ang-b.ang)!=)return a.ang<b.ang;

     return (a.a-b.a)*a.b<;

 }

 int n;

 P s[maxn];

 L l[maxn],q[maxn];P p[maxn];

 int h,r,tot,cnt;

 L get_line(P A,P B,P C,P D){

     L l;

     double a=-A.y-D.y+B.y+C.y;

     double b=-B.x-C.x+A.x+D.x;

     double c=-A.x*B.y-D.x*C.y+B.x*A.y+C.x*D.y;

     l.b=P(b,-a);

     if(sgn(a)!=)l.a=P(-c/a,);

     else l.a=P(,-c/b);

     return l;

 }

 void get_line(){

     for(int i=;i<=n;++i)

         l[++cnt]=get_line(s[],s[],s[i],s[i+]);

     for(int i=;i<=n;++i){

         l[++cnt].a=s[i];

         l[cnt].b=s[i+]-s[i];

     }

     for(int i=;i<=cnt;++i)

         l[i].ang=atan2(l[i].b.y,l[i].b.x);

 }

 P inter(L a,L b){

     P p=b.a-a.a;

     double t=(p*b.b)/(a.b*b.b);

     P ans;

     ans.x=a.a.x+a.b.x*t;

     ans.y=a.a.y+a.b.y*t;

     return ans;

 }

 bool jud(L a,L b,L c){

     P p=inter(a,b);

     return (p-c.a)*c.b>;

 }

 void get_Point(){

     sort(l+,l+cnt+);tot=;

     for(int i=;i<=cnt;++i)

         if(sgn(l[i].ang-l[i-].ang)!=)

             l[++tot]=l[i];

     cnt=tot;tot=,h=;

     q[++r]=l[];q[++r]=l[];

     for(int i=;i<=cnt;++i){

         if(sgn(q[r].b*q[r-].b)==)return;

         if(sgn(q[h].b*q[h+].b)==)return;

         while(h<r&&jud(q[r-],q[r],l[i]))r--;

         while(h<r&&jud(q[h+],q[h],l[i]))h++;

         q[++r]=l[i];

     }

     while(h<r&&jud(q[r-],q[r],q[h]))r--;

     while(h<r&&jud(q[h+],q[h],q[r]))h++;

     q[r+]=q[h];

     for(int i=h;i<=r;++i)

         p[++tot]=inter(q[i],q[i+]);

     p[++tot]=p[];

 }

 double get_S(P a[],int cnt){

     double ans=;

     if(cnt<)return ;

     for(int i=;i<cnt;++i){

         ans+=a[i]*a[i+];

     }

     ans=fabs(ans/);

     return ans;

 }

 void init(){

     scanf("%d",&n);

     for(int i=;i<=n;++i){

         int x,y;scanf("%d%d",&x,&y);

         s[i].x=x;s[i].y=y;

     }

     s[n+]=s[];

 }

 void work(){

     get_line();

     get_Point();

     S1=get_S(s,n+);

     S2=get_S(p,tot);

     ans=S2/S1;

     printf("%.4lf",ans);

 }

 int main(){

     init();

     work();

     return ;

 }