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#include <bits/stdc++.h>

using namespace std;

#define pb push_back
#define BP push_back
#define mp make_pair
#define MP make_pair
#define pbp(a, b) pb(mp(a, b))
#define PBP(a, b) PB(MP(a, b))
#define fst first
#define snd second
#define int4 int32_t
#define LL long long
#define int LL
#define FOR(i,a,b) for(int(i)=(a)-(int)((a)>(b));(i)!=(b)-(int)((a)>(b));(i)+=((a)<(b))?1:-1)
#define REP(b) FOR(i, 0, b)
#define REPI(i, b) FOR(i, 0, b)
#define REP1(b) FOR(i, 1, (b)+1)
#define REPI1(i, b) FOR(i, 1, (b)+1)
#define REV(b) FOR(i, b, 0)
#define REV1(b) FOR(i, (b)+1, 1)
#define ITER(j, b) for(auto (j) : (b))
#define ALL(x) (x).begin(), (x).end()
#define BOTH(x) (x).fst, (x).snd
#define sz(x) ((int)(x).size())
#define SZ(x) ((int)(x).size())
#define SKP(...) (__VA_ARGS__)
typedef vector<int> VI;
typedef pair<int,int> PII;
typedef long double LD;

template<class C> void minu(C& a4, C b4) { a4 = min(a4, b4); }
template<class C> void maxu(C& a4, C b4) { a4 = max(a4, b4); }

template<class TH> void _dbg(const char *sdbg, TH h)
{
    while(*sdbg==' ') sdbg++;
    if(*sdbg!='\"' && *sdbg!='\'' && (*sdbg!='S' || *(sdbg+1)!='K' || *(sdbg+2)!='P'))cerr<<" "<<sdbg<<"="<<h<<"\n";
    else cerr<<" "<<h<<"\n";
}
template<class TH, class... TA> void _dbg(const char *sdbg, TH h, TA... a)
{
    
    while(*sdbg==' ') sdbg++;
    if(*sdbg!='\"' && *sdbg!='\'' && (*sdbg!='S' || *(sdbg+1)!='K' || *(sdbg+2)!='P'))
    {
        cerr<<" ";
        while(*sdbg!=',')cerr<<*sdbg++;
        cerr<<"="<<h<<","; _dbg(sdbg+1, a...);
    }
    else
    {
        while(*sdbg!=',') sdbg++;
        cerr<<" "<<h<<","; _dbg(sdbg+1, a...);
    }
}

template<class T> ostream &operator<<(ostream &os, vector<T> V)
{
    os<<"[";for(auto vv:V)os<<vv<<",";return os<<"]";
} 

template<class L, class R> ostream &operator<<(ostream &os, pair<L,R> P)
{
    return os << "(" << P.fst << "," << P.snd << ")";
}

int XXXX_XXXX_XXXX;

#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define deb(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define scanf(...) (XXXX_XXXX_XXXX=scanf(__VA_ARGS__))
#else
#define debug(...) {}
#define cerr if(0)cout
#endif
struct XX_ld
{
    LD v;
    XX_ld(LD V) : v(V) {}
};
typedef XX_ld ld;

LD eps=1e-11;

inline ld operator +(ld a, ld b)
{
    return ld(a.v+b.v);
}

inline ld operator -(ld a, ld b)
{
    return ld(a.v-b.v);
}

inline ld operator -(ld a)
{
    return ld(-a.v);
}

inline ld operator *(ld a, ld b)
{
    return ld(a.v*b.v);
}

inline ld operator /(ld a, ld b)
{
    return ld(a.v/b.v);
}

inline bool operator ==(ld a, ld b)
{
    return a.v+eps >= b.v && a.v-eps <= b.v;
}

inline bool operator <(ld a, ld b)
{
    return a.v <= b.v && !(a == b);
}

inline bool operator >(ld a, ld b)
{
    return a.v >= b.v && !(a == b);
}

inline bool operator <=(ld a, ld b)
{
    return a.v <= b.v || (a == b);
}

inline bool operator >=(ld a, ld b)
{
    return a.v >= b.v || (a == b);
}

typedef pair <ld, ld> PLL;

int strona(PLL &a, PLL &b, PLL &c)
{
    ld tmp=a.fst*b.snd+b.fst*c.snd+c.fst*a.snd-(a.fst*c.snd+b.fst*a.snd+c.fst*b.snd);
    if(tmp>0) return -1;
    if(tmp<0) return 1;
    return 0;
}

ostream &operator<<(ostream &os, ld &b)
{
    return os << b.v;
}

bool gor_cmp(PLL a, PLL b)
{
    return mp(-a.fst.v, -a.snd.v) < mp(-b.fst.v, -b.snd.v);
}

bool dol_cmp(PLL a, PLL b)
{
    return mp(a.fst.v, a.snd.v) < mp(b.fst.v, b.snd.v);
}

ld przec(ld a1, ld b1, ld a2, ld b2)
{
    return (b2-b1)/(a1-a2);
}

ld pole(ld a1, ld b1, ld a2, ld b2, ld poc, ld kon) //1 to gora, 2 to dol
{
    //deb(a1, b1, a2, b2, poc, kon);
    if(poc>=kon) return 0;
    ld p1=a1*poc+b1;
    ld k1=a1*kon+b1;
    ld p2=a2*poc+b2;
    ld k2=a2*kon+b2;
    if(p1>=p2 && k1>=k2)
    {
        //deb("oba", p1, k1, p2, k2, SKP((kon-poc)*((p1-p2)+(k1-k2))/2));
        return (kon-poc)*((p1-p2)+(k1-k2))/2;
    }
    if(p1>=p2)
    {
        kon=przec(a1, b1, a2, b2);
        //deb("pie", p1, k1, p2, k2, kon, SKP((kon-poc)*((p1-p2)+(k1-k2))/2));
        return (kon-poc)*(p1-p2)/2;
    }
    if(k1>=k2)
    {
        poc=przec(a1, b1, a2, b2);
        //deb("dru", p1, k1, p2, k2, poc, SKP((kon-poc)*((p1-p2)+(k1-k2))/2));
        return (kon-poc)*(k1-k2)/2;
    }
    //deb(p1, k1, p2, k2);
    return 0;
}

int32_t main()
{
    
    int n;
    scanf("%lld", &n);
    vector <pair <PLL, PLL> > pary;
    vector <pair <PLL, int> > wieze;
    REP(n)
    {
        int a, b, c, d;
        scanf("%lld%lld%lld%lld", &a, &b, &c, &d);
        auto p1=mp(a, b), p2=mp(c, d);
        pary.pb(mp(p1, p2));
        wieze.pb(mp(p1, i));
        wieze.pb(mp(p2, i));
    }
    vector <pair <PLL, PLL> > ogr;
    REP(sz(wieze))
    {
        REPI(j, sz(wieze))
        {
            if(i!=j)
            {
                int str[n];
                FOR(x, 0, n) str[x]=0;
                bool nicprawo=1;
                ITER(w, wieze)
                {
                    //debug(i, j, wieze[i].fst, wieze[j].fst, w.fst, SKP(strona(wieze[i].fst, wieze[j].fst, w.fst)));
                    str[w.snd]+=strona(wieze[i].fst, wieze[j].fst, w.fst);
                    if(str[w.snd]==2) nicprawo=0;
                }
                if(nicprawo)
                {
                    ogr.pbp(wieze[i].fst, wieze[j].fst);
                }
            }
        }
    }
    //debug(ogr);
    ld ogrlew=-1000000;
    ld ogrpra=1000000;
    vector <PLL> gor, dol;
    ITER(par, ogr)
    {
        auto p1=par.fst, p2=par.snd;
        //debug(par);
        if(p1.fst==p2.fst)
        {
            if(p1.snd<p2.snd)
            {
                minu(ogrpra, p1.fst);
            }
            else
            {
                maxu(ogrlew, p1.fst);
            }
        }
        else if(p1.fst < p2.fst)
        {
            ld a=(p2.snd-p1.snd)/(p2.fst-p1.fst);
            dol.pbp(a, p1.snd-a*p1.fst);
        }
        else
        {
            ld a=(p2.snd-p1.snd)/(p2.fst-p1.fst);
            gor.pbp(a, p1.snd-a*p1.fst);
        }
    }
    //debug(dol);
    //debug(gor);
    sort(dol.begin(), dol.end(), dol_cmp);
    sort(gor.begin(), gor.end(), gor_cmp);
    //debug(dol);
    //debug(gor);
    {
        auto tmp=gor;
        gor.clear();
        int it=0;
        while(it<sz(tmp))
        {
            while(it+1<sz(tmp) && tmp[it].fst==tmp[it+1].fst) it++;
            gor.pb(tmp[it]);
            it++;
        }
    }
    {
        auto tmp=dol;
        dol.clear();
        int it=0;
        while(it<sz(tmp))
        {
            while(it+1<sz(tmp) && tmp[it].fst==tmp[it+1].fst) it++;
            dol.pb(tmp[it]);
            it++;
        }
    }
    //debug(dol);
    //debug(gor);
    ld inf=1e10;
    vector <pair <ld, PLL> > odol;
    odol.pbp(-inf, dol[0]);
    {
        int it=1;
        while(it<sz(dol))
        {
            ld pnt=przec(BOTH(odol.back().snd), BOTH(dol[it]));
            while(pnt<=odol.back().fst)
            {
                odol.pop_back();
                pnt=przec(BOTH(odol.back().snd), BOTH(dol[it]));
            }
            odol.pbp(pnt, dol[it]);
            it++;
        }
    }
    vector <pair <ld, PLL> > ogor;
    ogor.pbp(-inf, gor[0]);
    {
        int it=1;
        while(it<sz(gor))
        {
            ld pnt=przec(BOTH(ogor.back().snd), BOTH(gor[it]));
            while(pnt<=ogor.back().fst)
            {
                ogor.pop_back();
                pnt=przec(BOTH(ogor.back().snd), BOTH(gor[it]));
            }
            ogor.pbp(pnt, gor[it]);
            it++;
        }
    }
    //debug(ogor);
    //debug(odol);
    //debug(ogrlew);
    //debug(ogrpra);
    vector <pair <ld, int> > eves;
    ITER(i, ogor)
    {
        eves.pbp(i.fst, 0);
    }
    ITER(i, odol)
    {
        eves.pbp(i.fst, 1);
    }
    eves.pbp(ogrlew, 2);
    eves.pbp(ogrpra, 3);
    sort(eves.begin(), eves.end());
    bool bylo_lewo=0;
    bool bylo_prawo=0;
    ld last=-inf;
    ld wyn=0;
    int it1=-1;
    int it2=-1;
    //debug(eves);
    ITER(&eve, eves)
    {
        //debug(eve);
        int typ=eve.snd;
        ld akt=eve.fst;
        if(bylo_lewo) //ZLICZAJ
        {
            ld dod=pole(BOTH(ogor[it1].snd), BOTH(odol[it2].snd), last, akt);
            //debug("DODAJ", last, akt, it1, it2, dod);
            wyn=wyn+dod;
        }
        if(typ==0)
        {
            it1++;
        }
        if(typ==1)
        {
            it2++;
        }
        if(typ==2)
        {
            bylo_lewo=1;
        }
        if(typ==3)
        {
            bylo_prawo=1;
        }
        
        last=akt;
        if(bylo_prawo) break;
    }
    printf("%.20Lf\n", wyn.v);
}