#include <bits/stdc++.h>

using namespace std;

#define int long long
#define X first
#define Y second
typedef pair<int, int> pii;

const int N = 1e5 + 5;
int n;
vector<pii> edge;
vector<int> g[N];
int par[N], mark[N];

pii bfs(int u) {
  queue<pii> q;
  vector<int> vis(n + 1, 0);
  vis[u] = 1;
  q.push({u, 0});
  int len = 0, end = u;
  while (!q.empty()) {
    auto [v, dis] = q.front();
    q.pop();
    for (int x : g[v]) {
      if (!vis[x]) {
        vis[x] = 1;
        q.push({x, dis + 1});
        if (dis + 1 > len) {
          len = dis + 1;
          end = x;
        }
      }
    }
  }
  return {len, end};
}

void dfs(int u, int p) {
  par[u] = p;
  for (int v : g[u]) {
    if (v != p) dfs(v, u);
  }
}

void solve() {
  cin >> n;
  for (int i = 0, u, v; i < n - 1; i++) {
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
    edge.push_back({u, v});
  }
  int root = bfs(1).Y;
  auto [dia, leaf] = bfs(root);
  if (dia <= 2) {
    cout << "-1\n";
    return;
  }
  dfs(root, 0);
  int child;
  for (int i = 1; i <= n; i++) {
    if (par[i] == root) child = i;
  }
  for (int i = 0; i < n - 1; i++) {
    if (par[edge[i].X] == edge[i].Y) swap(edge[i].X, edge[i].Y);
  }
  int x = leaf;
  while (x != root) {
    mark[x] = 1;
    x = par[x];
  }
  bool flag1 = 0, flag2 = 0;
  for (int i = 0; i < n - 1; i++) {
    auto [a, b] = edge[i];
    if (flag1) {
      if (flag2 && mark[b]) {
        if (a == child) {
          cout << a << " " << leaf << "\n";
        } else {
          cout << a << " " << root << "\n";
        }
      } else {
        if (b == child) {
          cout << b << " " << leaf << "\n";
        } else {
          cout << b << " " << root << "\n";
        }
      }
    }
    else {
      if (mark[b]) {
        flag1 = true;
        if (b == child) {
          flag2 = true;
          cout << a << " " << leaf << "\n";
        } else {
          flag2 = false;
          cout << b << " " << root << "\n";
        }
      } else {
        cout << b << " " << root << "\n";
      }
    }
  }
}

signed main() {
  ios::sync_with_stdio(0); cin.tie(0);
  int T = 1;
  // cin >> T;
  while (T--) solve();
  return 0;
}