#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define pii pair<int,int>
#define fi first
#define se second
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

using namespace std;

main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n;
	cin>>n;
	vector< tuple<int,int,int,int> > v(n);
	vector<int> used(n,0);
	for(int i = 0; i < n; i++){
		int a,b,c;
		cin>>a>>b>>c;
		v[i] = make_tuple(a,b,c,i);
	}
	sort(v.begin(),v.end());
	map< pair<int,int>,vector<int> > m;
	for(int i = 0; i < n; i++){
		pair<int,int> t = {get<0>(v[i]),get<1>(v[i])};
		if(m.find(t)==m.end()) m[t] = vector<int>();
		m[t].pb(i);
	}
	for(auto t:m){
		//cout<<"x,y: "<<t.fi.fi<<" "<<t.fi.se<<" "<<endl;
		for(int i = 0; i+1 < t.se.size(); i+=2){
			//cout<<get<3>(v[t.se[i]])<<endl;
			cout<<get<3>(v[t.se[i]])+1<<" "<<get<3>(v[t.se[i+1]])+1<<"\n";
			used[get<3>(v[t.se[i]])] = 1;
			used[get<3>(v[t.se[i+1]])] = 1;
		}
	}
	vector<tuple<int,int,int,int> > v1;
	for(int i = 0; i < v.size(); i++){
		if(used[get<3>(v[i])]==0) v1.pb(v[i]);
	}
	map< int,vector<int> > m1;
	for(int i = 0; i < v1.size(); i++){
		if(m1.find(get<0>(v1[i]))==m1.end()){
			m1[get<0>(v1[i])] = vector<int>();
		}
		m1[get<0>(v1[i])].pb(i);
	}
	for(auto t:m1){
		for(int i = 0; i+1 < t.se.size(); i+=2){
			cout<<get<3>(v1[t.se[i]])+1<<" "<<get<3>(v1[t.se[i+1]])+1<<"\n";
			used[get<3>(v1[t.se[i]])] = 1;
			used[get<3>(v1[t.se[i+1]])] = 1;
		}
	}
	vector< tuple<int,int,int,int> > v2;
	for(int i = 0; i < v1.size(); i++){
		if(used[get<3>(v1[i])]==0){
			v2.pb(v1[i]);
		}
	}
	for(int i = 0; i < v2.size(); i+=2){
		cout<<get<3>(v2[i])+1<<" "<<get<3>(v2[i+1])+1<<"\n";
	}
}