#include <iostream>
#include <fstream>
#include <vector>
#include <random>
#include <algorithm>
#include <queue>
#include <string.h>
using namespace std;

typedef pair<int,int> PII;
typedef vector<int> VI;
typedef vector<pair<int,int>> VII;

vector<PII> ovojnica(int n, vector<PII> daljice) {
    vector<VI> adj(n+1);
    for (auto [a,b] : daljice) {
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    vector<PII> krog;
    auto [x,y] = daljice[0];
    krog.push_back({x,y});
    for (int it=1;it<daljice.size();it++) {
        int z1=adj[y][0], z2=adj[y][1];
        int z;
        if (z1!=x) z=z1; else z=z2;
        krog.push_back({y,z});
        x=y; y=z;
    }
    return krog;
}

int main() {
    vector<PII> daljice = {{2,5}, {7,10}, {3,5}, {3,10}, {7,2}};
    vector<PII> krog = ovojnica(12, daljice);
    for (PII s : krog) {
        cout << s.first << " " << s.second << endl;
    }
    return 0;
}