#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define SZ(a) ((int)a.size())
#define pb push_back
#define ALL(v) v.begin(), v.end()

pii edges[100005], ans[100005];
int indeg[100005], adj[100005], boss[100005], sz[100005];

int finds(int x) {
    while (x != boss[x]) x = boss[x];
    return x;
}

set<pii> vis;

void append(int i, int x, int y) {
    if (x > y) swap(x, y);
    ans[i] = pii(x, y);
    vis.insert(ans[i]);
}

bool conn(int x, int y) {
    if (x > y) swap(x, y);
    if (x == y) return 0;
    if (finds(x) == finds(y)) return 0;
    if (vis.find(pii(x, y)) != vis.end()) return 0;
    return 1;
}

vector<pair<int*, int>> stk[2];

bool Union(int x, int y) {
    x = finds(x), y = finds(y);
    if (x == y) return 0;
    if (sz[x] < sz[y]) swap(x, y);
    stk[0].pb(make_pair(&boss[y], boss[y])), boss[y] = x;
    stk[1].pb(make_pair(&sz[x], sz[x])), sz[x] += sz[y];
    return 1;
}

void undo() {
    for (int i = 0; i < 2; ++i)
        *stk[i].back().X = stk[i].back().Y, stk[i].pop_back();
}

int n, a, b;

void dq(int l, int r) {
    if (l == r) {
        /*cerr << l << ": ";
        for (auto e : vis)
            cerr << "(" << e.X << ", " << e.Y << ") ";
        cerr << endl;
        for (int i = 1; i <= n; ++i)
            cerr << finds(i) << " ";
        cerr << endl;*/
        if (conn(a, edges[l].X)) append(l, a, edges[l].X); 
        else if (conn(a, edges[l].Y)) append(l, a, edges[l].Y);
        else if (conn(b, edges[l].X)) append(l, b, edges[l].X);
        else if (conn(b, edges[l].Y)) append(l, b, edges[l].Y);
        else if (conn(a, b)) append(l, a, b);
        else assert(0);
        return;
    }
    int mid = (l + r) >> 1;
    int cur = SZ(stk[0]);
    for (int i = mid + 1; i <= r; ++i)
        Union(edges[i].X, edges[i].Y);
    dq(l, mid);
    while (SZ(stk[0]) > cur) undo();
    cur = SZ(stk[0]);
    for (int i = l; i <= mid; ++i)
        Union(ans[i].X, ans[i].Y);
    dq(mid + 1, r);
    while (SZ(stk[0]) > cur) undo();
}

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    cin >> n;
    iota(boss + 1, boss + n + 1, 1);
    fill(sz + 1, sz + n + 1, 1);
    for (int i = 1; i < n; ++i) {
        cin >> edges[i].X >> edges[i].Y;
        if (edges[i].X > edges[i].Y) swap(edges[i].X, edges[i].Y);
        vis.insert(edges[i]);
        ++indeg[edges[i].X];
        ++indeg[edges[i].Y];
        adj[edges[i].X] = edges[i].Y;
        adj[edges[i].Y] = edges[i].X;
    }
    if (*max_element(indeg + 1, indeg + n + 1) == n - 1)
        return cout << "-1\n", 0;
    for (int i = 1; i <= n; ++i)
        if (indeg[i] == 1) {
            if (a == 0) a = i;
            else if (adj[i] != adj[a]) {
                b = i;
                break;
            }
        }
    //cerr << a << " " << b << "\n";
    dq(1, n - 1);
    for (int i = 1; i < n; ++i)
        cout << ans[i].X << " " << ans[i].Y << "\n";
}