#include <bits/stdc++.h>

using namespace std;

#define iter(v) v.begin(), v.end()
#define SZ(v) (int)v.size()
#define pb emplace_back
#define ff first
#define ss second

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#ifdef LOCAL
void debug(){ cerr << "\n"; }
template<class T, class ... U>
void debug(T a, U ... b){ cerr << a << " ", debug(b...); }
template<class T> void pary(T l, T r){
    while(l != r) cerr << *l << " ", l++;
    cerr << "\n";
}
#else
#define debug(...) void()
#define pary(...) void()
#endif

template<class A, class B>
ostream& operator<<(ostream& o, pair<A, B> p){
    return o << '(' << p.ff << ',' << p.ss << ')';
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);


    int n;
    cin >> n;
    vector<vector<int>> g(n + 1);
    vector<int> deg(n + 1);
    vector<pii> e(n - 1);
    map<pii, int> id;
    vector<pii> ans;
    for (int i = 0;i < n - 1;i++) {
        int u, v;
        cin >> u >> v;
        e[i] = pii(u, v);
        g[u].push_back(v);
        g[v].push_back(u);
        deg[u]++;
        deg[v]++;
        id[pii(u, v)] = i;
        id[pii(v, u)] = i;
    }

    for(int i = 1; i <= n; i++){
        if(deg[i] == n - 1){
            cout << "-1\n";
            return 0;
        }
    }

    vector<int> root(n + 1), par(n + 1);
    function<void(int, int, int, int)> dfs = [&](int now, int p, int no, int rt){
        par[now] = p;
        root[now] = rt;
        for(int i : g[now]){
            if(i == p || i == no) continue;
            dfs(i, now, no, rt);
        }
    };

    int A = -1, B = -1;
    for(auto [u, v] : e){
        if(deg[u] == 1 || deg[v] == 1) continue;
        A = u; B = v;
        break;
    }
    dfs(A, A, B, A);
    dfs(B, B, A, B);
    int C = -1, D = -1;
    [&](){
        for(int i : g[A]){
            if(i == B) continue;
            for(int j : g[B]){
                if(j == A) continue;
                C = i;
                D = j;
                if(id[pii(A,C)] > id[pii(B,D)]) swap(A, B), swap(C, D);
                return;
            }
        }
    }();

    vector<pii> good = {pii(C, D), pii(A, D), pii(B, C)};
    set<pii> special;
    special.insert(pii(A, B));
    special.insert(pii(B, A));
    special.insert(pii(A, C));
    special.insert(pii(C, A));
    special.insert(pii(B, D));
    special.insert(pii(D, B));
    int cnt = 0;
    for(auto [u, v] : e){
        if(special.find(pii(u, v)) != special.end()){
            ans.pb(good[cnt++]);
            continue;
        }
        if(par[v] == u) swap(u, v);
        if(root[u] == A) ans.pb(pii(u, B));
        else ans.pb(pii(u, A));
    }

    for(auto [u, v] : ans) cout << u << " " << v << "\n";

}