#include <bits/stdc++.h>
	using namespace std;
	
	// Holi c:
	
	#define ll long long int
	#define fi first
	#define se second
	#define pb push_back
	#define all(v) v.begin(), v.end()
	
	const int Inf = 1e9;
	const ll mod = 1e9+7;
	const ll INF = 4e18;
	
	using ld = long double;
	const ld eps = 1e-6, inf = numeric_limits<ld>::max(), pi = acos(-1);
	bool geq(ld a, ld b){return a-b >= -eps;}
	bool leq(ld a, ld b){return b-a >= -eps;}
	bool ge(ld a, ld b){return a-b > eps;}
	bool le(ld a, ld b){return b-a > eps;}
	bool eq(ld a, ld b){return abs(a-b) <= eps;}
	bool neq(ld a, ld b){return abs(a-b) > eps;}

	struct point{
		ld x, y;
		point(): x(0), y(0){}
		point(ld x, ld y): x(x), y(y){}

		point operator+(const point & p) const{return point(x + p.x, y + p.y);}
		point operator-(const point & p) const{return point(x - p.x, y - p.y);}
		point operator*(const ld & k) const{return point(x * k, y * k);}
		point operator/(const ld & k) const{return point(x / k, y / k);}

		point operator+=(const point & p){*this = *this + p; return *this;}
		point operator-=(const point & p){*this = *this - p; return *this;}
		point operator*=(const ld & p){*this = *this * p; return *this;}
		point operator/=(const ld & p){*this = *this / p; return *this;}

		point rotate(const ld & a) const{return point(x*cos(a) - y*sin(a), x*sin(a) + y*cos(a));}
		point perp() const{return point(-y, x);}
		ld ang() const{
			ld a = atan2l(y, x); a += le(a, 0) ? 2*pi : 0; return a;
		}
		ld dot(const point & p) const{return x * p.x + y * p.y;}
		ld cross(const point & p) const{return x * p.y - y * p.x;}
		ld norm() const{return x * x + y * y;}
		ld length() const{return sqrtl(x * x + y * y);}
		point unit() const{return (*this) / length();}

		bool operator==(const point & p) const{return eq(x, p.x) && eq(y, p.y);}
		bool operator!=(const point & p) const{return !(*this == p);}
		bool operator<(const point & p) const{return le(x, p.x) || (eq(x, p.x) && le(y, p.y));}
		bool operator>(const point & p) const{return ge(x, p.x) || (eq(x, p.x) && ge(y, p.y));}
		bool half(const point & p) const{return le(p.cross(*this), 0) || (eq(p.cross(*this), 0) && le(p.dot(*this), 0));}
	};

	istream &operator>>(istream &is, point & p){return is >> p.x >> p.y;}
	ostream &operator<<(ostream &os, const point & p){return os << "(" << p.x << ", " << p.y << ")";}

	int sgn(ld x){
		if(ge(x, 0)) return 1;
		if(le(x, 0)) return -1;
		return 0;
	}
	
	bool pointInLine(const point & a, const point & v, const point & p){
		return eq((p - a).cross(v), 0);
	}
	
	bool pointInSegment(const point & a, const point & b, const point & p){
		return pointInLine(a, b - a, p) && leq((a - p).dot(b - p), 0);
	}

	point intersectLines(const point & a1, const point & v1, const point & a2, const point & v2){
		//lines a1+tv1, a2+tv2
		//assuming that they intersect
		ld det = v1.cross(v2);
		return a1 + v1 * ((a2 - a1).cross(v2) / det);
	}

	int intersectLineSegmentInfo(const point & a, const point & v, const point & c, const point & d){
		//line a+tv, segment cd
		point v2 = d - c;
		ld det = v.cross(v2);
		if(eq(det, 0)){
			if(eq((c - a).cross(v), 0)){
				return -1; //infinity points
			}else{
				return 0; //no point
			}
		}else{
			return sgn(v.cross(c - a)) != sgn(v.cross(d - a)); //1: single point, 0: no point
		}
	}

	vector<point> convexHull(vector<point> P){
		sort(P.begin(), P.end());
		vector<point> L, U;
		for(int i = 0; i < P.size(); i++){
			while(L.size() >= 2 && leq((L[L.size() - 2] - P[i]).cross(L[L.size() - 1] - P[i]), 0)){
				L.pop_back();
			}
			L.push_back(P[i]);
		}
		for(int i = P.size() - 1; i >= 0; i--){
			while(U.size() >= 2 && leq((U[U.size() - 2] - P[i]).cross(U[U.size() - 1] - P[i]), 0)){
				U.pop_back();
			}
			U.push_back(P[i]);
		}
		L.pop_back();
		U.pop_back();
		L.insert(L.end(), U.begin(), U.end());
		return L;
	}

	ld area(vector<point> & P){
		int n = P.size();
		ld ans = 0;
		for(int i = 0; i < n; i++){
			ans += P[i].cross(P[(i + 1) % n]);
		}
		return abs(ans / 2);
	}

	int intersectSegmentsInfo(const point & a, const point & b, const point & c, const point & d){
		point v1 = b - a, v2 = d - c;
		int t = sgn(v1.cross(c - a)), u = sgn(v1.cross(d - a));
		if(t == u){
			if(t == 0){
				if(pointInSegment(a, b, c) || pointInSegment(a, b, d) || pointInSegment(c, d, a) || pointInSegment(c, d, b)){
					return -1;
				}else{
					return 0;
				}
			}else{
				return 0;
			}
		}else{
			return sgn(v2.cross(a - c)) != sgn(v2.cross(b - c));
		}
	}

pair<vector<pair<point, point>>, vector<point>> precFunPolygon(vector<point> P){
	int n = P.size();
	vector<point> prov;
	vector<pair<point, point>> Lprov;
	for(int i = 0; i < n; i++){
		if(geq((P[(i + 1) % n] - P[i]).cross(P[(i + 2) % n] - P[i]), 0)){
			prov.pb(P[(i + 1) % n]); prov.pb(P[(i + 2) % n]);
			Lprov.pb({P[(i + 1) % n], P[(i + 2) % n]});
		}else{
			point at(INF, INF), seg;
			for(int j = 0; j < n; j++){
				if(j == i || j == (i + 1) % n || (j + 1) % n == i || (j + 1) % n == (i + 1) % n) continue;
				auto u = intersectLineSegmentInfo(P[i], P[(i + 1) % n] - P[i], P[j], P[(j + 1) % n]);
				if(u == 1){
					auto v = intersectLines(P[i], P[(i + 1) % n] - P[i], P[j], P[(j + 1) % n] - P[j]);
					if(le((P[i] - v).length(), (P[(i + 1) % n] - v).length())) continue;
					if(v == P[(j + 1) % n]) continue;
					if(v == P[j] && le((P[(i + 1) % n] - v).length(), (P[(i + 1) % n] - at).length())){
					    if(ge((v - P[(i + 1) % n]).cross(P[(j - 1 + n) % n] - P[(i + 1) % n]), 0)) at = v, seg = P[(j - 1 + n) % n];
					    if(ge((v - P[(i + 1) % n]).cross(P[(j + 1) % n] - P[(i + 1) % n]), 0)) at = v, seg = P[(j + 1) % n];					    
					}else if(le((P[(i + 1) % n] - v).length(), (P[(i + 1) % n] - at).length())){
					    if(ge((v - P[(i + 1) % n]).cross(P[j] - P[(i + 1) % n]), 0)) at = v, seg = P[j];
					    if(ge((v - P[(i + 1) % n]).cross(P[(j + 1) % n] - P[(i + 1) % n]), 0)) at = v, seg = P[(j + 1) % n];
					}
				}
			}
			prov.pb(P[(i + 1) % n]); prov.pb(at); prov.pb(seg);
			Lprov.pb({P[(i + 1) % n], at}); Lprov.pb({at, seg});
		}
	}
	sort(all(prov));
	prov.erase(unique(all(prov)), prov.end());
	return {Lprov, prov};
}

	pair<vector<vector<int>>, vector<point>> precFunPolygon1(vector<pair<point, point>> L, vector<point> P){
		int n = L.size();
		map<point, point> mp;
		map<point, vector<point>> mps;
		vector<pair<point, point>> Lprov;
		vector<point> prov;
		point minf(-Inf, -Inf);
		for(int i = 0; i < n; i++){
			point at = L[i].se;
			int l1 = -1;
			for(int j = 0; j < n; j++){
				if(L[i].fi == L[j].fi || L[i].fi == L[j].se || L[i].se == L[j].fi || L[i].se == L[j].se) continue;
				if(intersectSegmentsInfo(L[i].fi, L[i].se, L[j].fi, L[j].se) == 1){
					if(le((L[j].se - L[j].fi).cross(L[i].fi - L[j].fi), 0)) continue;
					auto it = intersectLines(L[i].fi, L[i].se - L[i].fi, L[j].fi, L[j].se - L[j].fi);
					if(it == at) continue;
					if(le((it - L[i].fi).length(), (at - L[i].fi).length())) at = it, l1 = j;
				}
			}
			if(at != L[i].se){
				int i1 = lower_bound(all(L), make_pair(L[i].fi, minf)) - L.begin(), i2 = lower_bound(all(L), make_pair(L[i].se, minf)) - L.begin();
				if(at != L[i].fi) Lprov.pb({L[i].fi, at});
				mps[L[l1].fi].pb(at);
				mp[L[i].fi] = at;	
				prov.pb(at); prov.pb(L[i].fi);
			}else{
			    prov.pb(L[i].fi); prov.pb(L[i].se);
				Lprov.pb({L[i].fi, L[i].se});
			}
		}
		for(auto e : mps){
			auto at = mp[e.fi];
			for(auto d : e.se){
				Lprov.pb({d, at});
			}
		}
		sort(all(prov));
		prov.erase(unique(all(prov)), prov.end());
		int k = prov.size();
		vector<vector<int>> Lf(k);
		for(int i = 0; i < Lprov.size(); i++){
			int i1 = lower_bound(all(prov), Lprov[i].fi) - prov.begin(), i2 = lower_bound(all(prov), Lprov[i].se) - prov.begin();
			Lf[i1].pb(i2);
		}
		return {Lf, prov};
	}

	vector<point> funPolygon(vector<vector<int>> L, vector<point> P, point p0){
		int n = P.size(); 
		int ini = lower_bound(all(P), p0) - P.begin();
		vector<int> res;
		vector<point> ans;
		vector<bool> fls(n, false);
		stack<int> q;
		q.push(ini); res.pb(ini);
		while(q.size()){
			int v = q.top();
			res.pb(v);
			q.pop();
			if(fls[v]){
				bool fl = false;
				for(int i = 0; i < res.size(); i++){
					if(res[i] == v) fl = true;
					if(fl) ans.pb(P[res[i]]);
				}
				break;
			}
			fls[v] = true;
			int u = L[v][0];
			q.push(u);
		}
		ans = convexHull(ans);
		return ans;
	}

	int main(){
		ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
		int n; cin>>n;
		vector<point> P(n);
		for(int i = 0; i < n; i++){
			int a, b; cin>>a>>b;
			P[i] = point(a, b);
		}
		vector<vector<int>> L0(n);
		auto vx = P;
		sort(all(vx));
		for(int i = 0; i < n; i++){
			L0[lower_bound(all(vx), P[i]) - vx.begin()].pb(lower_bound(all(vx), P[(i + 1) % n]) - vx.begin());
		}
		auto u = precFunPolygon(P);
		auto v = precFunPolygon1(u.fi, u.se);
		for(int i = 0; i < v.se.size(); i++){
		    //cout<<i<<" -> "<<v.se[i]<<" | ";
		}
		//cout<<'\n';
		for(int i = 0; i < v.fi.size(); i++){
		   // cout<<i<<" -> "<<v.fi[i][0]<<'\n';
		}
		vector<vector<point>> Ps;
		for(int i = 0; i < v.se.size(); i++){
			auto t = funPolygon(v.fi, v.se, v.se[i]);
			if(t.size() > 2) Ps.pb(t);
		}
		sort(all(Ps));
		Ps.erase(unique(all(Ps)), Ps.end());
		ld ans = 0;
		if(Ps.size()) ans = area(Ps[0]);
		for(auto e : Ps){
		  //  for(auto d : e) cout<<d<<" "; cout<<'\n';
		}
		if(Ps.size() > 1) ans = 0;
		cout<<setprecision(25)<<ans;
	}