#include<bits/stdc++.h>

#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)
#define EPS (1e-7)
#define COUNTER_CLOCKWISE 1
#define CLOCKWISE -1 
#define ONLINE_BACK 2
#define ONLINE_FRONT -2
#define ON_SEGMENT 0
#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 a){return Point(a*x,a*y);}
  Point operator / (double a){return Point(x/a,y/a);}
  bool operator < (const Point& p) const{ return !equals(x,p.x)?x<p.x:(!equals(y,p.y)&&y<p.y); }
  bool operator == (const Point& p)const{ return fabs(x-p.x) < EPS && fabs(y-p.y) < EPS; }
};

struct Segment{
  Point p1,p2;
  Segment(Point p1 = Point(),Point p2 = Point()):p1(p1),p2(p2){}
 bool operator == (const Segment& p)const { return ( p.p1 == p1 && p.p2 == p2 ) || ( p.p1 == p2 && p.p2 == p1 ); }
};

typedef Point Vector;
typedef Segment Line;

inline double dot(Point a,Point b){ return a.x*b.x + a.y*b.y; }
inline double cross(Point a,Point b){ return a.x*b.y - a.y*b.x; }
inline double norm(Point a){ return a.x*a.x+a.y*a.y; }
inline double abs(Point a){ return sqrt(norm(a)); }

int ccw(Point p0,Point p1,Point p2){
  Point a = p1-p0;
  Point b = p2-p0;
  if(cross(a,b) > EPS)return COUNTER_CLOCKWISE;
  if(cross(a,b) < -EPS)return CLOCKWISE;
  if(dot(a,b) < -EPS)return ONLINE_BACK;
  if(norm(a) < norm(b))return ONLINE_FRONT;
  return ON_SEGMENT;
}

bool intersectSS(Line s, Line t) {
  return ccw(s.p1,s.p2,t.p1)*ccw(s.p1,s.p2,t.p2) <= 0 &&
         ccw(t.p1,t.p2,s.p1)*ccw(t.p1,t.p2,s.p2) <= 0;
}

Point crosspoint(Line l,Line m){
  double A = cross(l.p2-l.p1,m.p2-m.p1);
  double B = cross(l.p2-l.p1,l.p2-m.p1);
  if(abs(A) < EPS && abs(B) < EPS){
    vector<Point> vec;
    vec.push_back(l.p1),vec.push_back(l.p2),vec.push_back(m.p1),vec.push_back(m.p2);
    sort(vec.begin(),vec.end());
    assert(vec[1] == vec[2]);
    return vec[1];
  }
  if(abs(A) < EPS)assert(false);
  return m.p1 + (m.p2-m.p1)*(B/A);
}

inline double cross3p(Point p,Point q,Point r){ return (r.x-q.x) * (p.y -q.y) - (r.y - q.y) * (p.x - q.x); }
inline bool collinear(Point p,Point q,Point r){ return fabs(cross3p(p,q,r)) < EPS; }
inline bool onSegment(Point p,Point q,Point r){
  return collinear(p,q,r) && equals(sqrt(pow(p.x-r.x,2)+pow(p.y-r.y,2)) + sqrt(pow(r.x-q.x,2) + pow(r.y-q.y,2) ),sqrt(pow(p.x-q.x,2)+pow(p.y-q.y,2)) ) ;
}

double getArea(vector<Point>& vec){
  double sum = 0;
  for(int i=0;i<(int)vec.size();i++) sum += cross(vec[i],vec[(i+1)%vec.size()]);
  return fabs(sum)/2.0;
}

int N;
vector<Point> ps;

Point vir;
bool comp_dist(const Point& a,const Point& b) { return !equals(abs(vir-a),abs(vir-b)) && abs(vir-a) < abs(vir-b); }

void makeSegments(vector<Segment> &segs){
  vector<Point> vp;
  rep(i,N-1) {
    vp.clear();
    vp.push_back(ps[i]);
    vp.push_back(ps[i+1]);
    Segment cur_seg = Segment(ps[i],ps[i+1]);
    rep(j,N-1) if( i != j ) {
      Segment seg = Segment(ps[j],ps[j+1]);
      if( equals(cross(cur_seg.p1-cur_seg.p2,seg.p1-seg.p2),0.0) ) {
        if( onSegment(cur_seg.p1,cur_seg.p2,seg.p1) ) vp.push_back(seg.p1);
        if( onSegment(cur_seg.p1,cur_seg.p2,seg.p2) ) vp.push_back(seg.p2);
      } else if( intersectSS(seg,cur_seg) )  vp.push_back(crosspoint(cur_seg,seg));
    }
    vir = ps[i];
    sort(vp.begin(),vp.end(),comp_dist);
    vp.erase(unique(vp.begin(),vp.end()),vp.end());
    rep(j,(int)vp.size()-1) segs.push_back(Segment(vp[j],vp[j+1]));
  }
}

vector<Point> angle_ps;

struct Data{ 
  int from,to,rev; 
  bool operator < (const Data & a)const{
    Vector vec_a = angle_ps[a.to] - angle_ps[a.from];
    Vector vec_b = angle_ps[to] - angle_ps[from];
    double arg_a = atan2(vec_b.y,vec_b.x);
    double arg_b = atan2(vec_a.y,vec_a.x);
    return !equals(arg_a,arg_b) && arg_a < arg_b;
  }
};

vector<vector<Data> > G;
vector<Point> vp;

void makeGraph(const vector<Segment> &segs){
  map<Point,int> mp;
  int V = 0;
  rep(i,segs.size()) if( !mp.count(segs[i].p1) ) mp[segs[i].p1] = V++;
  if( !mp.count(segs.back().p2) ) mp[segs.back().p2] = V++;
  vp.resize(V);
  for(map<Point,int>::iterator it = mp.begin(); it != mp.end(); it++){
    vp[it->second] = it->first;
  }
  angle_ps = vp;
  G.resize(V,vector<Data>());
  rep(i,segs.size()) {
    int s = mp[segs[i].p1], t = mp[segs[i].p2];
    G[s].push_back((Data){s,t,-1});
    G[t].push_back((Data){t,s,-1});
  }

  rep(i,V) sort(G[i].begin(),G[i].end());
  rep(i,V) rep(j,(int)G[i].size()) if( G[i][j].rev == -1 ) {
    int to = G[i][j].to;
    rep(k,(int)G[to].size())if( G[to][k].to == i ){
      G[i][j].rev = k;
      G[to][k].rev = j;
      break;
    }
  }
}

const int MAX_V = 5000;
bool visited[MAX_V][MAX_V];

bool getPath(int start_node,int node,int edge,vector<Point> &buf){
  if( visited[node][edge] ){
    if( !buf.empty() && node == start_node ) return true;
    return false;
  }
  visited[node][edge] = true;
 
  int next_node = G[node][edge].to;
  int next_edge = (G[node][edge].rev+1)%((int)G[next_node].size());
  buf.push_back(vp[G[node][edge].from]);
  if(getPath(start_node,next_node,next_edge,buf)) return true;
  else return visited[node][edge] = false;
}

void compute(){
  vector<Segment> segs;
  segs.clear();
  makeSegments(segs);
  makeGraph(segs);
  segs.clear();
  ps.clear();
  angle_ps.clear();
  int V = vp.size();
  rep(i,V) rep(j,V) visited[i][j] = false;
  double area = 0;
  rep(i,V) rep(j,(int)G[i].size()) if( !visited[i][j] ){
    vector<Point> buf;
    if( getPath(i,i,j,buf) && !buf.empty() ) area += getArea(buf);
  }
  printf("%.10lf\n",area/2.0);  
}

int main(){
  scanf("%d",&N);
  ps.resize(N);
  rep(i,N) scanf("%lf %lf",&ps[i].x,&ps[i].y);
  compute();
  return 0;
}

Measured memory_bytes: 16156