//контест не оч :c
#ifdef DEBUG
#include "./bits.cpp"
using namespace std;
#define dbg(x) ;
#else
#include<bits/stdc++.h>
using namespace std;
#define dbg(x) cout << #x << ':' << x
#endif
#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
#pragma GCC optimize("fast-math")
// #define endl '\n'
#define int long long
#define pt pair<int, int>
#define x first
#define y second

struct ev{
    int x, y, z;
    int i;
    bool operator<(const ev &oth) const{
        if(x == oth.x){
            if(y == oth.y){
                return z < (oth.z);
            }
            return (y) < (oth.y);
        }
        return (x) < (oth.x);
    }
};

signed main() {
#ifdef DEBUG
    // freopen("input.txt", "r", stdin);
    // freopen("05.txt", "w", stdout);
#else
    // freopen(".in", "r", stdin);
    // freopen(".out", "w", stdout);
#endif
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin >> n;
    vector<ev> a(n);
    for(int i = 0; i < n; i++){
        cin >> a[i].x >> a[i].y >> a[i].z;
        a[i].i = i;
    }
    sort(a.begin(), a.end());
    int sv = -1, sy = -1;
    vector<int> v(n, 0);
    for(int i = 0; i < n; i+=2){
        if(i + 1 < n && a[i].x == a[i + 1].x){
            if(a[i].y == a[i + 1].y){
                v[a[i].i] += 1;
                v[a[i + 1].i] += 1;
                cout << a[i].i + 1 << ' ' << a[i + 1].i + 1 << endl;
                if(sv != -1 && sy != -1){
                    v[a[sv].i] += 1;
                    v[a[sy].i] += 1;
                    cout << a[sv].i + 1 << ' ' << a[sy].i + 1 << endl;
                    sv = -1;
                    sy = -1;
                }
            }
            else {
                if(sy == -1){
                    sy = i;
                }
                else{
                    v[a[i].i]++;
                    v[a[sy].i]++;
                    cout << a[i].i + 1 << ' ' << a[sy].i + 1 << endl;
                    sy = -1;
                }
                i--;
            }
        }
        else{
            if(sv == -1 && sy != -1){
                sv = sy;
                sy = -1;
            }
            if(sv == -1)
                sv = i;
            else{
                v[a[i].i] += 1;
                v[a[sv].i] += 1;
                cout << a[i].i + 1 << ' ' << a[sv].i + 1 << endl;
                sv = -1;
            }
            i--;
        }
    }
    int l = -1;
    for(int i = 0; i < n; i++){
        if(!v[i]){
            if(l == -1) l = i;
            else {
                v[l] += 1;
                v[i] += 1;
                cout << l + 1 << ' ' << i + 1 << endl;
                l = -1;
            }
        }
    }
    for(int i = 0; i < n; i++) assert(v[i] == 1);
}