#include <bits/stdc++.h>

using namespace std;

int64_t inf = 1000 * 1000 * 1000;
int64_t inf64 = inf * inf;
int64_t mod = 228228227;
int64_t nll = 0;

#define se second
#define fi first

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    cerr << fixed << setprecision(8);
    srand(time(0));
    auto START_TIME = chrono::high_resolution_clock::now();

    map<int64_t, map<int64_t, vector<pair<int64_t, int64_t> > > > mp;
    int32_t n;
    cin >> n;
    for (int32_t i = 0; i < n; ++i)
    {
        int32_t a, b, c;
        cin >> a >> b >> c;
        mp[c][b].emplace_back(a, i + 1);
    }
    vector<int64_t> ans;
    for (auto &c : mp)
    {
        for (auto &cc : c.se)
        {
            cout << "Z:" << c.fi << " Y:" << cc.fi << ":   ";
            sort(cc.se.begin(), cc.se.end());
            for (int32_t i = 0; i < cc.se.size(); ++i)
            {
                cout << "(" << cc.se[i].fi << " " << cc.se[i].se << ")    ";
                //ans.push_back(cc.se[i].se);
            }
            while (cc.se.size() > 1)
            {
                ans.emplace_back(cc.se.back().se);
                cc.se.pop_back();
                ans.emplace_back(cc.se.back().se);
                cc.se.pop_back();
            }
            cout << endl;
        }
    }
    for (auto &c : mp)
    {
        for (auto &cc : c.se)
        {
            //cout << "Z:" << c.fi << " Y:" << cc.fi << ":   ";
            sort(cc.se.begin(), cc.se.end());
            for (int32_t i = 0; i < cc.se.size(); ++i)
            {
                //cout << "(" << cc.se[i].fi << " " << cc.se[i].se << ")    ";
                ans.push_back(cc.se[i].se);
            }
            while (cc.se.size() > 1)
            {
                ans.emplace_back(cc.se.back().se);
                cc.se.pop_back();
                ans.emplace_back(cc.se.back().se);
                cc.se.pop_back();
            }
            //cout << endl;
        }
    }
    for (int32_t i = 0; i < n; i += 2)
    {
        cout << ans[i] << " " << ans[i + 1] << endl;
    }

    cerr << endl << chrono::duration<long double>(chrono::high_resolution_clock::now() - START_TIME).count() << " sec.";
}