#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

template<class T> int sgn(T x){ return (x > 0) - (x < 0); }
template<class T>
struct Point{
    typedef Point P;
    T x, y;
    explicit Point(T x = 0, T y = 0): x(x), y(y){}
    bool operator<(P p) const { return tie(x, y) < tie(p.x, p.y);}
    bool operator==(P p) const { return tie(x, y) == tie(p.x, p.y); }
    P operator-(P p) const {return P(x - p.x, y - p.y);}
    T cross(P p) const {return x * p.y - y * p.x;}
    T cross(P a, P b) const {return (a - *this).cross(b - *this);}
};

const int N = 2e5 + 3;

int n;
ll x1[N], y1[N], x2[N], y2[N];

#define all(x) (x).begin(), (x).end()

typedef Point<ll> P;
vector<P> convexHull(vector<P> pts) {
    if(pts.size() <= 1) return pts;
    sort(all(pts));
    vector<P> h((int)pts.size() + 1);
    int s = 0, t = 0;
    for(int it = 2; it--; s = --t, reverse(all(pts))){
        for(P p: pts){
            while(t >= s + 2 && h[t - 2].cross(h[t - 1], p) <= 0) t--;
            h[t++] = p;
        }
    }
    return {h.begin(), h.begin() + t - (t == 2 && h[0] == h[1])};
}

template<class P>
int sideOf(P s, P e, P p){ return sgn(s.cross(e, p)); }

bool inHull(const vector<P> &l, P p, bool strict = true){
    int a = 1, b = (int)l.size() - 1, r = !strict;
    if(sideOf(l[0], l[a], l[b]) > 0) swap(a, b);
    if(sideOf(l[0], l[a], p) >= r || sideOf(l[0], l[b], p) <= -r)
        return false;
    while(abs(a - b) > 1){
        int c = (a + b) / 2;
        (sideOf(l[0], l[c], p) > 0 ? b : a) = c;
    }
    return sgn(l[a].cross(l[b], p)) < r;
}

bool check(const vector<Point<ll>> &in, const vector<Point<ll>> &out){
    vector<Point<ll>> ch = convexHull(in);

    for(auto p: out){
        if(inHull(ch, p, true))
            return false;
    }
    return true;
}


int main(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> n;
    for(int i = 0; i < n; ++i)
        cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];

    if(n <= 2){
        cout << "possible\n";
        return 0;
    }

    vector<Point<ll>> in1, in2, out1, out2;
    for(int i = 0; i < n; ++i){
        in1.push_back(Point<ll>(x1[i], y1[i]));
        in2.push_back(Point<ll>(x1[i], y2[i]));
        out1.push_back(Point<ll>(x2[i], y2[i]));
        out2.push_back(Point<ll>(x2[i], y1[i]));
    }

    if(check(in1, out1) || check(in2, out2))
        cout << "possible\n";
    else
        cout << "impossible\n";
}

answer.code:23:15: error: ‘ll y1 [200003]’ redeclared as different kind of entity
   23 | ll x1[N], y1[N], x2[N], y2[N];
      |               ^
In file included from /usr/include/features.h:461,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/c++config.h:571,
                 from /usr/include/c++/11/cassert:43,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/stdc++.h:33,
                 from answer.code:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:221:1: note: previous declaration ‘double y1(double)’
  221 | __MATHCALL (y1,, (_Mdouble_));
      | ^~~~~~~~~~
answer.code: In function ‘int main()’:
answer.code:74:29: warning: pointer to a function used in arithmetic [-Wpointer-arith]
   74 |         cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
      |                             ^
answer.code:74:22: error: no match for ‘operator>>’ (operand types are ‘std::basic_istream<char>::__istream_type’ {aka ‘std::basic_istream<char>’} and ‘double(double) noexcept’)
   74 |         cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
      |         ~~~~~~~~~~~~ ^~ ~~~~~
      |             |               |
      |             |               double(double) noexcept
      |             std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}
In file included from /usr/include/c++/11/sstream:38,
                 from /usr/include/c++/11/complex:45,
                 from /usr/include/c++/11/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/stdc++.h:54,
                 from answer.code:1:
/usr/include/c++/11/istream:120:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  120 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/11/istream:120:7: note:   conversion of argument 1 would be ill-formed:
answer.code:74:29: error: invalid conversion from ‘double (*)(double) noexcept’ to ‘std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)’ {aka ‘std::basic_istream<char>& (*)(std::basic_istream<char>&)’} [-fpermissive]
   74 |         cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
      |                         ~~~~^
      |                             |
      |                             double (*)(double) noexcept
In file included from /usr/include/c++/11/sstream:38,
                 from /usr/include/c++/11/complex:45,
                 from /usr/include/c++/11/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/stdc++.h:54,
                 from answer.code:1:
/usr/include/c++/11/istream:124:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]’ (near match)
  124 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/11/istream:124:7: note:   conversion of argument 1 would be ill-formed:
answer.code:74:29: error: invalid conversion from ‘double (*)(double) noexcept’ to ‘std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)’ {aka ‘std::basic_ios<char>& (*)(std::basic_ios<char>&)’} [-fpermissive]
   74 |         cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
      |                         ~~~~^
      |                             |
      |                             double (*)(double) noexcept
In file included from /usr/include/c++/11/sstream:38,
                 from /usr/include/c++/11/complex:45,
                 from /usr/include/c++/11/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/stdc++.h:54,
                 from answer.code:1:
/usr/include/c++/11/istream:131:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ (near match)
  131 |       operator>>(ios_base& (*__pf)(ios_base&))
      |       ^~~~~~~~
/usr/include/c++/11/istream:131:7: note:   conversion of argument 1 would be ill-formed:
answer.code:74:29: error: invalid conversion from ‘double (*)(double) noexcept’ to ‘std::ios_base& (*)(std::ios_base&)’ [-fpermissive]
   74 |         cin >> x1[i] ...