#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define all(v) (v).begin(), (v).end()

void run() {
	ll n;
	cin >> n;
	vii A(n);
	for (ll i = 0; i < n; i++) {
		ll a, b;
		cin >> a >> b;
		A[i] = {a, b};
	}
	sort(all(A));
	if (n%2 == 1) {
		cout << "impossible" << endl;
		return;
	}
	ll a = A[0].x + A[n-1].x, b = A[0].y + A[n-1].y;
	for (ll i = 0; 2*i < n; i++) {
		if (A[i].x + A[n-1-i].x != a || A[i].y + A[n-1-i].y != b) {
			cout << "impossible" << endl;
			return;
		}
	}
	cout << "possible" << endl;
}

signed main() {
    ios_base::sync_with_stdio(false); cin.tie(0);
    run();
    return 0;
}