#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define all(x) ((x).begin()), ((x).end())
typedef long double D;
typedef long long LL;
const LL inf = 1e9 + 7;
const int N = 200022;
struct P {
	LL x, y;
	P operator + (const P & b) const { return P{x + b.x, y + b.y}; }
	P operator - (const P & b) const { return P{x - b.x, y - b.y}; }
	LL operator * (const P & b) const { return x * b.y - y * b.x; }
	bool operator < (const P & b) const { return x < b.x || x == b.x && y < b.y; }
};
P operator * (const LL & a, const P & b) {
	return P{a * b.x, a * b.y};
}
int x[N][2], y[N][2];
void yes() {
	printf("possible\n");
	exit(0);
}
void no() {
	printf("impossible\n");
	exit(0);
}
int main() {
	int n;
	scanf("%d", &n);
	LL xmin = -inf, xmax = inf, ymin = -inf, ymax = inf;
	for(int i = 0; i < n; i++) {
		scanf("%d%d%d%d", &x[i][0], &y[i][0], &x[i][1], &y[i][1]);
		if(x[i][0] > xmin) {
			xmin = x[i][0];
		}
		if(x[i][1] < xmax) {
			xmax = x[i][1];
		}
		if(y[i][0] > ymin) {
			ymin = y[i][0];
		}
		if(y[i][1] < ymax) {
			ymax = y[i][1];
		}
	}
	if(xmin <= xmax || ymin <= ymax) {
		yes();
	}
	for(int d = 0; d < 2; d++) {
		vector<P> a[2];
		for(int i = 0; i < n; i++) {
			a[0].pb({x[i][0], y[i][1]});
			a[1].pb({x[i][1], y[i][0]});
		}
		bool flag = true;
		for(int e = 0; e < 2; e++) {
			sort(all(a[0]));
			vector<P> vec;
			for(auto p : a[0]) {
				while(vec.size() >= 2 && (p - vec.back()) * (vec.back() - vec[(int)vec.size() - 2]) >= 0) {
					vec.pop_back();
				}
				vec.pb(p);
			}
			vec.insert(vec.begin(), P{-inf, vec[0].y});
			vec.pb(P{vec.back().x, inf});
			for(auto p : a[1]) {
				int pos = lower_bound(all(vec), P{p.x, -inf}) - vec.begin();
				if(pos == vec.size()) {
					
				}else {
					if(vec[pos].x == p.x) {
						if(p.y > vec[pos].y) {
							flag = false;
							break;
						}
					}else {
						P a = vec[pos - 1];
						P b = vec[pos];
						if(p.y * (b.x - a.x) > a.y * (b.x - a.x) + (b.y - a.y) * (p.x - a.x)) {
							flag = false;
							break;
						}
					}
				}
			}

			swap(a[0], a[1]);
			for(int f = 0; f < 2; f++) {
				for(auto & p : a[f]) {
					p = -1 * p;
				}
			}
		}
		if(flag) yes();
		for(int i = 0; i < n; i++) {
			y[i][0] *= -1;
			y[i][1] *= -1;
			swap(y[i][0], y[i][1]);
		}
	}
	no();
}