#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;
}

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> cutPolygon(const vector<point> & P, const point & a, const point & v){
	//returns the part of the convex polygon P on the left side of line a+tv
	int n = P.size();
	vector<point> lhs;
	for(int i = 0; i < n; ++i){
		if(geq(v.cross(P[i] - a), 0)){
			lhs.push_back(P[i]);
		}
		if(intersectLineSegmentInfo(a, v, P[i], P[(i+1)%n]) == 1){
			point p = intersectLines(a, v, P[i], P[(i+1)%n] - P[i]);
			if(p != P[i] && p != P[(i+1)%n]){
				lhs.push_back(p);
			}
		}
	}
	return lhs;
}

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);
}

pair<vector<vector<int>>, 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(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());
	int k = prov.size();
	vector<vector<int>> L(k);
	for(int i = 0; i < Lprov.size(); i++){
		auto it = lower_bound(all(prov), Lprov[i].fi) - prov.begin(), at = lower_bound(all(prov), Lprov[i].se) - prov.begin();
		L[it].pb(at);
	}
	return {L, 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);
	}
	auto u = precFunPolygon(P);
    vector<vector<point>> Ps;
    for(int i = 0; i < n; i++){
        Ps.pb(funPolygon(u.fi, u.se, P[i]));
    }
    sort(all(Ps));
    Ps.erase(unique(all(Ps)), Ps.end());
    //for(auto e : Ps[0]) cout<<e<<" "; cout<<'\n';
    auto ans = area(Ps[0]);
	if(Ps.size() > 1) ans = 0;
    cout<<setprecision(25)<<ans;
}