#include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <ctime>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <set>
#include <map>
#include <iostream>
#include <deque>
#include <complex>
#include <string>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <valarray>
#include <unordered_map>
#include <iterator>
#include <assert.h>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) (container).begin(), (container).end()
#define RALL(container) (container).rbegin(), (container).rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

namespace geom{
#define X real()
#define Y imag()
#define at(i) ((*this)[i])
#define SELF (*this)
	enum {TRUE = 1, FALSE = 0, BORDER = -1};
	typedef int BOOL;
	typedef double R;
	const R INF = 1e8;
	const R EPS = 1e-8;
	const R PI = 3.1415926535897932384626;
	inline int sig(const R &x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
	inline BOOL less(const R &x, const R &y) {return sig(x-y) ? x < y : BORDER;}
	typedef complex<R> P;
	inline R norm(const P &p){return p.X*p.X+p.Y*p.Y;}
	inline R inp(const P& a, const P& b){return (conj(a)*b).X;}
	inline R outp(const P& a, const P& b){return (conj(a)*b).Y;}
	inline P unit(const P& p){return p/abs(p);}
	inline P proj(const P &s, const P &t){return t*inp(s, t)/norm(t);}
	inline int ccw(const P &s, const P &t, const P &p, int adv=0){
		int res = sig(outp(t-s, p-s));
		if(res || !adv) return res;
		if(sig(inp(t-s, p-s)) < 0) return -2;	// p-s-t
		if(sig(inp(s-t, p-t)) < 0) return 2;	// s-t-p
		return 0;								// s-p-t
	}
	
	
	struct L : public vector<P>{	// line
		L(const P &p1, const P &p2){this->push_back(p1);this->push_back(p2);}
		L(){}
		P dir()const {return at(1) - at(0);}
		BOOL online(const P &p)const {return !sig(outp(p-at(0), dir()));}
	};
	struct S : public L{	// segment
		S(const P &p1, const P &p2):L(p1, p2){}
		S(){}
		BOOL online(const P &p)const {
			if(!sig(norm(p - at(0))) || !sig(norm(p - at(1)))) return BORDER;
			return !sig(abs(at(0)-p) + abs(at(1) - p) - abs(at(0) - at(1)));
		}
	};
	struct C : public P{
		C(){}
		C(const P& p, const R r):P(p), r(r){}
		R r;
		BOOL inside(const P& p)const { return less(norm(p-SELF), r*r);}
	};
	struct F : public C{
		R s, t;
		int cc;
		F(const C &c, R ss, R tt, int cc=1):C(c), s(ss), t(tt),cc(cc){
			if(PI < s) s -= 2*PI;
			if(PI < t) t -= 2*PI;
		}
		R length(){
			return ((t < s) ? t - (s-2*PI) : t-s) * r;
		}
		BOOL inside(const P& p)const {
			P v = p - SELF;
			R a = arg(v);
			if(t < s){
				return less(s, a) || less(a, t);
			}else{
				return less(s, a) && less(a, t);
			}
		}
	};

	inline P proj(const P &s, const L &t){return t[0] + proj(s-t[0], t[1]-t[0]);}
	inline P crosspoint(const L &l, const L &m){
		R A = outp(l.dir(), m.dir()), B = outp(l.dir(), l[1] - m[0]);
		if(!sig(abs(A)) && !sig(abs(B))) return m[0]; // same line
		if(abs(A) < EPS) assert(false); // !!!PRECONDITION NOT SATISFIED!!!
		return m[0] + B / A * (m[1] - m[0]);
	}
	vector<L> CommonTangent(C c1, C c2){
		if(c1.r > c2.r) swap(c1, c2);
		double d = abs(c1-c2);
		vector<L> res;
		if(d < EPS) return res;
		if(d + EPS > c1.r + c2.r){
			// テ・ツ??ヲツ篠・テァツキツ?
			P crs = (c1*c2.r + c2*c1.r) / (c1.r + c2.r);
			double rad = asin(c1.r/abs(crs-c1));
			res.push_back(L(crs, crs + (c1-crs)*polar(1., rad)));
			res.push_back(L(crs, crs + (c1-crs)*polar(1., -rad)));
		}
		if(c1.r + d + EPS > c2.r){
			// テ・ツ、ツ姪ヲツ篠・テァツキツ?
			double rad = 0.5*PI+asin((c2.r-c1.r) / d);
			P v = unit(c2-c1)*polar(1., rad);
			if(c1.r + d - EPS < c2.r){
				res.push_back(L(c1+v*c1.r, c1+v*c1.r+(c1-c2)*P(0, 1)));
			}else{
				res.push_back(L(c1+v*c1.r, c2+v*c2.r));
				v = 2.*proj(v, c2-c1) - v;
				res.push_back(L(c1+v*c1.r, c2+v*c2.r));
			}
		}
		return res;
	}

#undef SELF
#undef at
}

using namespace geom;


namespace std{
	bool operator<(const P &a, const P &b){return abs(a.X-b.X) > EPS ? a.X < b.X : a.Y+EPS < b.Y;}
	bool operator==(const P &a, const P &b){return !sig(norm(a-b));}
	istream& operator>>(istream &is, P &p){R x,y;is>>x>>y;p=P(x, y);return is;}
	istream& operator>>(istream &is, L &l){l.resize(2);return is >> l[0] >> l[1];}
	istream& operator>>(istream &is, C &c){return is >> (P &)c >> c.r;}
}

int n;

R dijkstra(const vector< vector<pair<int, R>> > &g, int start){
	int n = g.size();
	vector<R> ret(n, INF);
	priority_queue<pair<R, int>, vector<pair<R, int>>, greater<pair<R, int>> > dp;
	dp.push(pair<R, int>(0., start));
	while(!dp.empty()){
		int s = dp.top().second;
		R c = dp.top().first;
		dp.pop();
		if(s == start && c != 0) return c;
		if(s != start && ret[s] < c - EPS) continue;
		FOR(it, g[s]){
			int t = it->first;
			if(ret[t] - EPS > c+it->second){
				ret[t] = c+it->second;
				dp.push(pair<R, int>(ret[t], t));
			}
		}
	}
	return INF;
}


int main(){
	ios::sync_with_stdio(false);
	cin >> n;
	vector<pair<pair<P, P>, double>> e;
	vector<P> p;
	P fst, prev;
	vector<S> s(n);
	REP(i, n)cin >> s[i];
	vector<F> f;
	REP(i, n){
		const S &cur = s[i];
		const S &nxt = s[(i+1) % n];
		C c;
		(P&)c = sig(outp(cur.dir(), nxt.dir())) ? 
			   crosspoint(L(cur[1], cur[1]+cur.dir()*P(0, 1)), L(nxt[0], nxt[0]+nxt.dir()*P(0, 1)))
			: (cur[1] + nxt[0]) * .5;
		c.r = abs(cur[1] - c);
		R ca = arg(cur[1] - c);
		R cb = arg(nxt[0] - c);
		int cc = ccw(cur[0], cur[1], c);
		if(cc == -1) swap(ca, cb);
		f.emplace_back(c, ca, cb, cc);
		p.push_back(cur[0]);
		p.push_back(cur[1]);
		p.push_back(cur[0]+P(1000, 0));
		p.push_back(cur[1]+P(1000, 0));
		e.emplace_back(mp(cur[0], cur[1]), abs(cur.dir()));
		e.emplace_back(mp(cur[1]+P(1000, 0), cur[0]+P(1000, 0)), abs(cur.dir()));
		e.emplace_back(mp(cur[1], nxt[0]), f.back().length());
	}
	REP(i, n)REP(j, n)if(i!=j){
		const F &u = f[i];
		const F &v = f[j];
		vector<L> ls = CommonTangent(u, v);
		FOR(s, ls){
			S root(proj(u, *s), proj(v, *s));
			if(!u.inside(root[0]) || !v.inside(root[1])) continue;
			int f1 = ccw(root[0], root[1], u) != u.cc;
			int f2 = ccw(root[0], root[1], v) != v.cc;
			p.push_back(root[0]);
			p.push_back(root[1]);
			p.push_back(root[0]+P(1000, 0));
			p.push_back(root[1]+P(1000, 0));
			e.emplace_back(mp(root[0]+(f1?P(1000, 0):P(0,0)), 
							  root[1]+(f2?P(1000, 0):P(0,0))), abs(root.dir()));
			e.emplace_back(mp(root[1]+(!f2?P(1000, 0):P(0,0)), 
							  root[0]+(!f1?P(1000, 0):P(0,0))), abs(root.dir()));
		}
	}
	sort(ALL(p));UNIQUE(p);
	
	REP(i, n){
		vector<pair<R, int>> q;
		P st = s[i][1] - f[i];
		REP(j, p.size()) if(f[i].inside(p[j]) && !sig(norm(f[i]-p[j]) - f[i].r*f[i].r)){
			R ar = sig(norm(p[j]-s[i][1])) ? arg(((p[j]-f[i])/st) * P(-1, 0)) : f[i].cc == 1 ? -PI : PI;
			q.emplace_back(ar, j);
		}
		if(f[i].cc == 1) sort(ALL(q));
		else sort(RALL(q));
		REP(j, (int)q.size() - 1){
			e.emplace_back(mp(p[q[j].second], p[q[j+1].second]), f[i].r * abs(q[j].first - q[j+1].first));
			e.emplace_back(mp(p[q[j+1].second]+P(1000, 0), p[q[j].second]+P(1000, 0)), f[i].r * abs(q[j].first - q[j+1].first));
		}
	}
	
	n = p.size();
	vector<vector<pair<int, R>>> g(n);
	int start = lower_bound(ALL(p), s[0][0]) - p.begin();
	sort(ALL(e));UNIQUE(e);
	FOR(it, e){
		int u = lower_bound(ALL(p), it->first.first) - p.begin();
		int v = lower_bound(ALL(p), it->first.second) - p.begin();
		g[u].emplace_back(v, it->second);
	}
	
	printf("%.14f\n", dijkstra(g, start));
	return 0;
}

Measured memory_bytes: 4528