#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

const int N = 100447;
vector<PII> g[N];
int deg[N];
PII ans[N];
int root = 0;
int u = -1;
int n;


void dfs(int v, int idx, int h = 0)
{
	if (h == 0)
	{
		sort(ALL(g[v]), [&](PII a, PII b)
		{
			return deg[a.first] > deg[b.first];
		});
	}
	if (h >= 2)
	{
		if (u == -1) u = v;
		ans[idx] = {root, v};
	}
	int pr = -1, pi = -1;
	int mx = 0;
	for (auto& [to, i] :g[v])
	{
		mx = max(mx, i);
		if (i != idx)
		{
			dfs(to, i, h + 1);
			if (h == 0 && pr != -1)
			{
				ans[pi] = {pr, to};
			}
			pi = i;
			pr = to;
		}
	}
	if (h == 0)
	{
		ans[pi] = {pr, u};
		FOR (i, mx + 1, n)
		{
			if (ans[i] == MP(root, u))
			{
				swap(ans[i], ans[mx]);
				break;
			}
		}
	}
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	cin >> n;
	FOR (i, 0, n - 1)
	{
		int a, b;
		cin >> a >> b;
		a--, b--;
		g[a].PB({b, i});
		g[b].PB({a, i});
		deg[a]++, deg[b]++;
	}
	if (*max_element(deg, deg + n) == n - 1)
	{
		cout << -1 << '\n';
		return 0;
	}
	while (deg[root] == 1) root++;
	
	dfs(root, -1, 0);
	
	FOR (i, 0, n - 1)
	{
		cout << ans[i].first + 1 << ' ' << ans[i].second + 1 << '\n';
	}
	
	return 0;
}