#pragma warning(disable : 4996) //_CRT_SECURE_NO_WARNINGS
#include <iomanip>
#include <stdio.h>
#include <map>
#include <ctime>
#include <queue>
#include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <algorithm>
#include <fstream>
#include <set>
#include <list>
#define sync ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define ss second
#define ff first
#define ll long long
#define mp make_pair
#define endl "\n"
#define pb push_back
#define ld long double
#define M_PI 3.14159265358979323846
const ld EPS = 0.0001;
const ll INF = 1000000007;
using namespace std;

int get_int(string s)
{
	int coef = 1;
	int res = 0;
	for (int i = s.size() - 1; i >= 0; i--)
	{
		res += ((int)(s[i] - '0'))*coef;
		coef *= 10;
	}
	return res;
}

deque<int> get_deque(string s)
{
	string n="";
	deque<int> ans;
	for (int i = 0; i < s.size(); i++)
	{
		if (s[i] == ' ')
		{
			ans.pb(get_int(n)-1);
			n = "";
		}
		else
			n += s[i];
	}
	if (n!="")
		ans.pb(get_int(n)-1);
	n = "";
	return ans;
}

int main()
{
	int n;
	cin >> n;
	string c;
	getline(std::cin, c);
	vector<deque<int> > a(n);
	int k = 0;
	for (int i = 0; i < n; i++)
	{
		string s;
		getline(std::cin, s);
		a[i]=get_deque(s);
		k += a[i].size();
	}
	//k /= 2;
	vector<deque<int> > b = a;
	/*for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < b[i].size(); j++)
			cout << b[i][j]<<' ';
		cout << endl;
	}*/
	for (int h = 0; h < k; h++)
	{
		for (int i = 0; i < n; i++)
		{
			if (a[i].size()!=0)
			{
				if (a[a[i].front()].size()!=0)
				{
					//cout << i << ' ' << a[a[i].front()].front() << endl;
					if (i == a[a[i].front()].front())
					{
						cout << min(a[i].front(), a[a[i].front()].front()) + 1 << ' ' << max(a[i].front(), a[a[i].front()].front()) + 1 << endl;
						a[a[i].front()].pop_front();
						a[i].pop_front();
					}
				}
			}
		}
	}
}