#include <bits/stdc++.h>
 
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
 
mt19937 rng((int) chrono::steady_clock::now().time_since_epoch().count());
    
const int MOD = 1e9 + 7;
const int MAXN = 1e5 + 5;
const ll INF = 2e18;

vector<int> v[MAXN];
int n;
 
pii bfs(int node) {
    queue<pii> q;
	vector<int> check(n+1);
	check[node] = 1;
	q.push({node, 0});
	int resp = 0, fim = node;
	while (!q.empty()) {
		pii atual = q.front();
		q.pop();
		for (int x : v[atual.first]) {
			if (!check[x]) {
				check[x] = 1;
				q.push({x, atual.second+1});
				if (atual.second + 1 > resp) {
					resp = atual.second + 1;
					fim = x;
				}
			}
		}
	}
	return {resp, fim};
}

int pai[MAXN], mark[MAXN];

void dfs(int node, int p) {
    pai[node] = p;
    for (int x : v[node]) {
        if (x != p) dfs(x, node);
    }
}

vector<pii> ed;
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int a, b;
	cin >> n;
	for (int i = 0; i < n - 1; i++) {
		cin >> a >> b;
        ed.push_back({a, b});
		v[a].push_back(b);
		v[b].push_back(a);
	}
	int root = bfs(1).second, filho;
    int diametro = bfs(root).first;
    int fim = bfs(root).second; 
    if (diametro <= 2) {
        cout << "-1\n";
        return 0;
    }
    dfs(root, 0);
    for (int i = 1; i <= n; i++) {
        if (pai[i] == root) filho = i;
    }
    for (int i = 0; i < n - 1; i++) {
        if (pai[ed[i].first] == ed[i].second) swap(ed[i].first, ed[i].second);
    }
    int x = fim;
    while (x != root) {
        mark[x] = 1;
        x = pai[x];
    }
    bool ja = false, inv = false;
    for (int i = 0; i < n - 1; i++) {
        a = ed[i].first, b = ed[i].second;
        if (!ja) {
            if (mark[b]) {
                ja = true;
                if (b == filho) {
                    inv = true;
                    cout << a << ' ' << fim << '\n';
                }
                else {
                    inv = false;
                    cout << b << ' ' << root << '\n';
                }
            }
            else {
                cout << b << ' ' << root << '\n';
            }
        }
        else {
            if (inv) {
                cout << a << ' ' << root << '\n';
            }
            else {
                if (b == filho) {
                    cout << b << ' ' << fim << '\n';
                }
                else {
                    cout << b << ' ' << root << '\n';
                }
            }
        }
    }
    return 0;
}