#include <bits/stdc++.h>

#define f first
#define s second
#define pb push_back
#define mp make_pair

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

const int N = 300500, inf = 1e9, mod = 998244353;
const ll INF = 1e18;

int sum(int a, int b) {
    a += b;
    if (a >= mod)
        a -= mod;
    return a;
}

int sub(int a, int b) {
    a -= b;
    if (a < 0)
        a += mod;
    return a;
}

int mult(int a, int b) {
    return 1ll * a * b % mod;
}

int bp(int a, int b) {
    int res = 1;
    while (b) {
        if (b & 1)
            res = mult(res, a);
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

int inv(int x) {
    return bp(x, mod - 2);
}
int n;
const int maxN = 2e5 + 10;
int x[maxN][2];
int y[maxN][2];
bool cmp(tuple<ll,ll,int>& a, tuple<ll,ll,int>& b) {
    ll X1 = get<0>(a);
    ll Y1 = get<1>(a);
    ll X2 = get<0>(b);
    ll Y2 = get<1>(b);
    assert(X1 > 0 && Y1 > 0 && X2 > 0 && Y2 > 0);
    return (X1 * Y2 < X2 * Y1);
}
bool check() {
    vector<int> lower(n), upper(n);
    iota(lower.begin(), lower.end(), 1);
    iota(upper.begin(), upper.end(), 1);
    sort(lower.begin(), lower.end(), [&](int i, int j) {
        return make_pair(x[i][0], y[i][0]) < make_pair(x[j][0], y[j][0]);
    });

    sort(upper.begin(), upper.end(), [&](int i, int j) {
        return make_pair(x[i][1], y[i][1]) < make_pair(x[j][1], y[j][1]);
    });

    vector<pair<ll,ll>> pt_l, pt_u;
    for (int id : lower) {
        ll X = x[id][0];
        ll Y = y[id][0];
        while (!pt_l.empty() && pt_l.back().second <= Y) {
            pt_l.pop_back();
        }
        while (pt_l.size() >= 2) {
            auto t1 = pt_l[pt_l.size() - 2];
            auto t2 = pt_l.back();
            if ((t2.second - Y) * (t2.first - t1.first) > (X - t2.first) * (t1.second - t2.second)) {
                break;
            }
            else {
                pt_l.pop_back();
            }
        }
        pt_l.emplace_back(X, Y);
    }

    for (int id : upper) {
        ll X = x[id][1];
        ll Y = y[id][1];
        if (!pt_u.empty() && pt_u.back().second <= Y) {
            continue;
        }
        while (pt_u.size() >= 2) {
            auto t1 = pt_u[pt_u.size() - 2];
            auto t2 = pt_u.back();
            if ((t2.second - Y) * (t2.first - t1.first) < (X - t2.first) * (t1.second - t2.second)) {
                break;
            }
            else {
                pt_u.pop_back();
            }
        }
        pt_u.emplace_back(X, Y);
    }
//    for (auto& it : pt_l) {
//        cout << it.first << " " << it.second << endl;
//    }
    vector<tuple<ll, ll, int>> events;
    for (int i = 0; i + 1 < pt_l.size(); i++) {
        events.emplace_back(pt_l[i].second - pt_l[i + 1].second, pt_l[i + 1].first - pt_l[i].first, i);
    }
    for (int i = 0; i + 1 < events.size(); i++) {
        assert(cmp(events[i], events[i + 1]));
    }
    for (int i = (int)pt_u.size() - 2; i >= 0; i--) {
        events.emplace_back(pt_u[i].second - pt_u[i + 1].second, pt_u[i + 1].first - pt_u[i].first, ~i);
    }
    sort(events.begin(), events.end(), cmp);
    int ID_U = pt_u.size() - 1;
    int ID_L = 0;
    ll PRV_A = 0;
    ll PRV_B = 1;
    for (auto& it : events) {
        ll A = get<0>(it);
        ll B = get<1>(it);
        if (PRV_A * pt_l[ID_L].first + PRV_B * pt_l[ID_L].second <= PRV_A * pt_u[ID_U].first + PRV_B * pt_u[ID_U].second) {
            return true;
        }
        if (A * pt_l[ID_L].first + B * pt_l[ID_L].second <= A * pt_u[ID_U].first + B * pt_u[ID_U].second) {
            return true;
        }
        if (get<2>(it) >= 0) {
            ID_L++;
        }
        else {
            ID_U--;
        }
        PRV_A = A;
        PRV_B = B;
    }
    assert(ID_L == pt_l.size() - 1);
    assert(ID_U == 0);
    PRV_A = 1;
    PRV_B = 0;
    if (PRV_A * pt_l[ID_L].first + PRV_B * pt_l[ID_L].second <= PRV_A * pt_u[ID_U].first + PRV_B * pt_u[ID_U].second) {
        return true;
    }
    return false;


}
mt19937 rnd(228);
void solve() {
    cin >> n;
//    n = rnd() % 10 + 1;
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < 2; j++) {
            cin >> x[i][j] >> y[i][j];
        }
//        ll A = rnd() % 10 + 1;
//        ll B = A + rnd() % 10 + 1;
//        x[i][0] = A;
//        x[i][1] = B;
//        A = rnd() % 10 + 1;
//        B = A + rnd() % 10 + 1;
//        y[i][0] = A;
//        y[i][1] = B;
    }
    for (int iter = 0; iter < 2; iter++) {
        if (check()) {
            cout << "possible\n";
            return ;
        }

        for (int i = 1; i <= n; i++) {
            swap(y[i][0], y[i][1]);
            y[i][0] *= -1;
            y[i][1] *= -1;
        }
    }
    cout << "impossible\n";
}

int main() {
#ifdef DEBUG
    freopen("input.txt", "r", stdin);
#endif
    ios_base::sync_with_stdio(false);
    int t = 1;
//    cin >> t;
    for (int i = 1; i <= t; i++) {
//        cout << "Case #" << i << endl;
        solve();
    }
}