#include <iostream>
#include <map>

using namespace std;

int main() {
    long long n;
    cin >> n;

    long long sb = 0, sp = 0;

    map<pair<long long, long long>, long long> scores;

    if (n % 2 == 1) {
        cout << "impossible" << endl;
        return 0;
    }

    for (long long i = 0; i < n; i++) {
        long long b, p;
        cin >> b >> p;
        sb += b;
        sp += p;
        scores[make_pair(b, p)]++;
    }

    if (sb % (n / 2) != 0) {
        cout << "impossible" << endl;
        return 0;
    }
    if (sp % (n / 2) != 0) {
        cout << "impossible" << endl;
        return 0;
    }

    sb = sb / (n / 2);
    sp = sp / (n / 2);

    for (auto it = scores.begin(); it != scores.end(); it++) {
        auto other = make_pair(sb - it->first.first, sp - it->first.second);
        if (scores[other] != it->second) {
            cout << "impossible" << endl;
            return 0;
        }
    }

    cout << "possible" << endl;

    return 0;
}