#include<bits/stdc++.h>
using namespace std;
#define int long long
const int maxN = 1e5 + 69;
struct vl {
	int x, y;
	size_t operator() (const vl& p) const {
		return (p.x << 32) ^ p.y;
	}
	bool operator == (const vl& oth) const {
		return x == oth.x && y == oth.y;
	}
};
int n;
int u[maxN], v[maxN];
unordered_set<vl, vl> us;
set<int> adj[maxN];
mt19937 rng(time(NULL));
void dfs(int u, int p, vector<int>& res, int& cnt) {
	res.push_back(u);
	cnt--;
	if (cnt <= 0) return;
	for (int v : adj[u])
	if (v != p) dfs(v, u, res, cnt);
}
vector<int> getsome(int u) {
	int cnt = 20;
	vector<int> res;
	dfs(u, u, res, cnt);
	return res;
}
signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	cin >> n;
	us.reserve(maxN);
	for (int i = 1; i <= n - 1; i++) {
		cin >> u[i] >> v[i];
		adj[u[i]].insert(v[i]);
		adj[v[i]].insert(u[i]);
		us.insert({min(u[i], v[i]), max(u[i], v[i])});
	} 
	vector<int> ans;
	for (int i = 1; i <= n - 1; i++) {
		if (adj[u[i]].size() <= 1 && adj[v[i]].size() <= 1)
			return cout << -1, 0;
		adj[u[i]].erase(v[i]);
		adj[v[i]].erase(u[i]);

		vector<int> lolu = getsome(u[i]);
		vector<int> lolv = getsome(v[i]);
		shuffle(lolu.begin(), lolu.end(), rng);
		shuffle(lolv.begin(), lolv.end(), rng);
		
		int xu = -1, xv;
		for (int yu : lolu)
		for (int yv : lolv)
		if (!us.count({min(yu, yv), max(yu, yv)})) {
			xu = yu;
			xv = yv;
			goto flag;
		}
		flag:;
		if (xu == -1) {
			return cout << -1, 0;
		}

		adj[xu].insert(xv);
		adj[xv].insert(xu);
		ans.push_back(xu);
		ans.push_back(xv);
		// cout << xu << ' ' << xv << '\n';
	}
	for (int i = 0; i < ans.size(); i += 2)
		cout << ans[i] << ' ' << ans[i + 1] << '\n';
}