#include <bits/stdc++.h>
#define ll long long
using namespace std;
 
int n, u, v; 
string s;
 
int main()
{
    cin >> n; 
    set<pair<int, int>>sp;
    cin.ignore();
 
    for(int i = 1; i <= n; ++i){
        getline(cin, s);
        stringstream ss(s);
        ss >> u; 
        int a = i;
        if(a > u)
            swap(a, u);
        sp.insert({a, u});
        while(ss >> v){
            int a = i, b = v;
            if(a > b) swap(a, b); 
            sp.insert({a, b});
        }
    }
    for(auto i : sp)
        cout << i.first << " " << i.second << endl;
    return 0;
}

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MwoyIDMKMSAzCjEgMg==

3
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1 3
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