#include <bits/stdc++.h>
#define ff first
#define ss second
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int SZ = 101010;

int n, u[SZ], v[SZ], deg[SZ];
vector<int> g[SZ];

int dep[SZ], par[SZ], son[SZ], chk[SZ];
void dfs(int p, int v) {
	for (int x : g[v]) if (p != x) {
		dep[x] = dep[v] + 1;
		par[x] = v;
		son[v] = x;
		dfs(v, x);
	}
}

int main() {
	cin.tie(0); ios_base::sync_with_stdio(0);
	
	cin >> n;
	for (int i = 0; i < n - 1; i++) {
		cin >> u[i] >> v[i];
		deg[u[i]]++;
		deg[v[i]]++;
		g[u[i]].push_back(v[i]);
		g[v[i]].push_back(u[i]);
	}

	for (int i = 1; i <= n; i++) if (deg[i] == n - 1) return !(cout << "-1\n");

	int pos = -1;
	for (int i = 1; i <= n; i++) {
		if (deg[i] == 1 && !chk[i]) {
			dep[i] = 0;
			dfs(-1, i);

			int pos = g[i][0];
			int can = -1;

			set<int> st;
			for (int x : g[pos]) st.insert(x);

			vector<pii> V;
			bool flag = true;
			for (int j = 0; j < n - 1; j++) {
				int x = u[j];
				int y = v[j];

				if (dep[x] > dep[y]) swap(x, y);
				
				if (y != pos) {
					V.push_back({i, y});
					if (son[y]) can = son[y];
					else if (st.find(y) == st.end()) can = y;
				}
				else {
					if (can == -1) {
						for (int x : g[pos]) chk[x] = true;
						flag = false;
						break;
					}
					else {
						V.push_back({pos, can});
					}
				}
			}
			if (flag) {
				for (auto [x, y] : V) {
					cout << x << ' ' << y << '\n';
				}
				return 0;
			}
		}
	}
	assert(false);
}