#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 zisk
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);
    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]++;
    }

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

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

    dfs(rt, rt, -1, rt);

    vector<pii> ans;
    bool leaf = true;
    int A = -1, B = -1;
    set<int> qq;
    for(int i : g[rt]) qq.insert(i);
    for(auto [u, v] : e){
        debug("solve", u, v);
        if(!leaf){
            if(dpt[u] < dpt[v]) swap(u, v);
            debug("del", u, v, dpt[u], dpt[v]);
            if(root[u] == A) ans.pb(pii(u, B)), debug(u, B);
            else ans.pb(pii(u, A)), debug(u, A);
            continue;
        }
        
        if(deg[u] > 1 && deg[v] > 1){
            bool ok = false;
            for(int i : g[u]){
                if(i == v || del[i]) continue;
                for(int j : g[v]){
                    if(j == u || del[j]) continue;
                    debug("owo", i, j);
                    ans.pb(pii(i, j));
                    ok = true;
                    dpt[i] = dpt[j] = 0;
                    dfs(i, i, v, i);
                    dfs(j, j, u, j);
                    pary(iter(dpt));
                    pary(iter(root));
                    leaf = false;
                    A = i; B = j;
                    break;
                }
                if(ok) break;
            }
            continue;
        }

        if(deg[u] == 1 && deg[v] == 1 && u == rt) swap(u, v);
        else if(deg[v] == 1) swap(u, v);
        del[u] = true;
        deg[v]--;

        if(par[u] != rt){
            ans.pb(pii(u, rt));
            continue;
        }
        qq.erase(u);
        if(!qq.empty()){
            ans.pb(pii(u, *qq.begin()));
            continue;
        }
        
        bool ok = false;
        int c = -1;
        for(int i = 1; i <= n; i++){
            if(par[i] == u) c = i;
            if(i != rt && i != u && par[i] != u && par[i] != rt){
                ans.pb(pii(u, i));
                ok = true;
                break;
            }
        }
        if(!ok){
            assert(c != -1);
            for(int i = 1; i <= n; i++){
                if(par[i] == rt && i != u){
                    ans.pb(pii(i, c));
                    ok = true;
                    break;
                }
            }
        }
        assert(ok);

    }

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