#include<bits/stdc++.h>
#define f first
#define s second
#define mp make_pair
#define pi M_PI
#define inf 1e14
#define eps (1e-5)
#define MAX 200000
#define equals(a,b) (fabs((a)-(b))<eps)
using namespace std;
 
class Point{
public:
  double x,y;
  Point(double x=0,double y=0):x(x),y(y){}
 
  Point operator+(Point p){ return Point(x+p.x,y+p.y);}
  Point operator-(Point p){ return Point(x-p.x,y-p.y);}
  Point operator*(double k){ return Point(x*k,y*k);}
  Point operator/(double k){ return Point(x/k,y/k);}
  bool operator<(Point p)const{ return (x!=p.x ? x<p.x : y<p.y);}
  bool operator==(Point p)const{ return fabs(x-p.x)<eps && fabs(y-p.y)<eps;}
 
  double abs(){ return sqrt(norm());}
  double norm(){ return (x*x+y*y);}
};
typedef Point Vector;
typedef vector<Point> Polygon;
 
class Segment{
public:
  Point p1,p2;
  Segment(Point p1=Point(),Point p2=Point()):p1(p1),p2(p2){}
};
typedef Segment Line;
 
double norm(Vector a){ return (a.x*a.x+a.y*a.y);}
double abs(Vector a){ return sqrt(norm(a));}
double dot(Vector a,Vector b){ return (a.x*b.x+a.y*b.y);}
double cross(Vector a,Vector b){ return (a.x*b.y-a.y*b.x);}
 
bool isParallel(Segment s,Segment t){
  return equals(cross(s.p1-s.p2,t.p1-t.p2),0.0);
}
 
int ccw(Point p0,Point p1,Point p2){
  Vector a=p1-p0;
  Vector b=p2-p0;
  if(cross(a,b)>eps)return 1;
  if(cross(a,b)<-eps)return -1;
  if(dot(a,b)<-eps)return 2;
  if(a.norm()<b.norm())return -2;
  return 0;
}
 
bool intersect(Point p1,Point p2,Point p3,Point p4){
  return (ccw(p1,p2,p3)*ccw(p1,p2,p4)<=0 &&
          ccw(p3,p4,p1)*ccw(p3,p4,p2)<=0);
}
 
bool intersect(Segment s1,Segment s2){
  return intersect(s1.p1,s1.p2,s2.p1,s2.p2);
}
 
Point getCrossPointLL(Line a,Line b){
  double A=cross(a.p2-a.p1,b.p2-b.p1);
  double B=cross(a.p2-a.p1,a.p2-b.p1);
  if(abs(A)<eps || abs(B)<eps)return b.p1;
  return b.p1+(b.p2-b.p1)*(B/A);
}
 
double getPolygonArea(Polygon p){
  double area=0.0;
  int n=p.size();
  for(int i=0;i<n;i++)area+=cross(p[i%n],p[(i+1)%n]);
  return area/2;
}
 
typedef vector<vector<int> > Graph;
 
Graph SegmentArrangement(vector<Segment> v,vector<Point> &ps){
  for(int i=0;i<v.size();i++){
    ps.push_back(v[i].p1);
    ps.push_back(v[i].p2);
    for(int j=i+1;j<v.size();j++){
      if(intersect(v[i],v[j]))
        ps.push_back(getCrossPointLL(v[i],v[j]));
    }
  }
  sort(ps.begin(),ps.end());
  ps.erase(unique(ps.begin(),ps.end()),ps.end());
  Graph g(ps.size());
  for(int i=0;i<v.size();i++){
    vector<pair<double,int> > list;
    for(int j=0;j<ps.size();j++)
      if(ccw(v[i].p1,v[i].p2,ps[j])==0)
        list.push_back(mp(norm(v[i].p1-ps[j]),j));
    sort(list.begin(),list.end());
    for(int j=0;j+1<list.size();j++){
      int a=list[j].s,b=list[j+1].s;
      g[a].push_back(b);
      g[b].push_back(a);
    }
  }
  return g;
}
 
bool merge_if_able(Segment &s,Segment t) {
  if(!isParallel(s,t))return false;
  if(abs(ccw(s.p1,s.p2,t.p1))==1 || 
     abs(ccw(s.p1,s.p2,t.p2))==1)return false;
  if(ccw(s.p1,s.p2,t.p1)==-2 || 
     ccw(t.p1,t.p2,s.p1)==-2)return false;
  s=Segment(min(s.p1,t.p1),max(s.p2,t.p2));
  return true;
}
 
void merge(vector<Segment>& v) {
  for(int i=0;i<v.size();i++){
    if(v[i].p2<v[i].p1)swap(v[i].p2,v[i].p1);
  }
  for(int i=0;i<v.size();i++){
    for(int j=i+1;j<v.size();j++){
      if(merge_if_able(v[i],v[j])){
        v[j--]=v.back();
        v.pop_back();
      }
    }
  }
}
 
Graph e;
vector<Segment> vs;
vector<Point> vp;
Polygon p;
int start=-1;
double ans=0.0;
 
double getAngle(Vector a,Vector b){
  double tmp=dot(a,b)/(abs(a)*abs(b));
  if(tmp<-1.0)tmp=-1.0;
  if(1.0<tmp)tmp=1.0;
  double r=acos(tmp)*180.0/pi;
  if(cross(a,b)<-eps)r=360.0-r;
  return r;
}
 
void dfs(int now,int before){
  if(now==start)return;
  pair<double,int> pdi(inf,-1);
  for(int i=0;i<e[now].size();i++){
    int next=e[now][i];
    double ang=getAngle(vp[before]-vp[now],vp[next]-vp[now]);
    if(next==before)ang=361;
    pdi=min(pdi,mp(ang,next));
  }
  p.push_back(vp[now]);
  dfs(pdi.s,now);
  return;
}
 
int main()
{
  int n,a,b,c,d;
 
  cin>>n;
  cin>>a>>b;
  for(int i=1;i<n;i++){
    cin>>c>>d;
    vs.push_back(Segment(Point(a,b),Point(c,d)));
    a=c;b=d;
  }
  merge(vs);
  e=SegmentArrangement(vs,vp);
  Point s(inf,inf);
  for(int i=0;i<vp.size();i++)s=min(s,vp[i]);
  for(int i=0;i<vp.size();i++)if(vp[i]==s)start=i;
  for(int i=0;i<e[start].size();i++){
    p.clear();
    p.push_back(vp[start]);
    dfs(e[start][i],start);
    double res=getPolygonArea(p);
    if(0.0<=res)ans+=res;
  }
  printf("%.10f\n",ans);
  return 0;
}


Measured memory_bytes: 3780