#include<bits/stdc++.h>

#define int long long
#define pb push_back
#define fi first
#define se second
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxN = 1e6 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;
int n;
vector<int> adj[maxN];
int jump[maxN][20];
int depth[maxN];
pair<int, int> edge[maxN];
int mark[maxN];
void ReadInput()
{
    cin >> n;
    for(int i=1; i<=2*n-3; i++)
    {
        int u, v;
        cin >> u >> v;
        edge[i] = {u, v};
    }
}
void dfs(int u, int par)
{
    for(int v : adj[u])
    {
        if(v == par) continue;
        jump[v][0] = u;
        depth[v] = depth[u] + 1;
        for(int i=1; i<=18; i++)
            jump[v][i] = jump[jump[v][i - 1]][i - 1];
        dfs(v, u);
    }
}
int lca(int u, int v)
{
    if(depth[u] < depth[v]) swap(u, v);
    int k = depth[u] - depth[v];
    for(int i=18; i>=0; i--)
        if(k >> i & 1) u = jump[u][i];
    if(u == v) return u;
    for(int i=18; i>=0; i--)
        if(jump[u][i] != jump[v][i])
        {
            u = jump[u][i];
            v = jump[v][i];
        }
    return jump[u][0];
}
int dist(int u, int v)
{
    return depth[u] + depth[v] - 2 * depth[lca(u, v)];
}
int lab[maxN];
int findset(int u)
{
    return lab[u] < 0 ? u : lab[u] = findset(lab[u]);
}
int unite(int u, int v)
{
    int r = findset(u), s = findset(v);
    if(r == s) return false;
    if(lab[r] < lab[s]) swap(r, s);
    lab[r] += lab[s];
    lab[s] = r;
    return true;
}
void go(int x, int y)
{
    vector<int> vc1, vc2;
    int t = lca(x, y);
    while(x != t)
    {
        vc1.pb(x);
        x = jump[x][0];
    }
    while(y != t)
    {
        vc2.pb(y);
        y = jump[y][0];
    }
    vc2.pb(t);
    reverse(vc2.begin(), vc2.end());
    for(int v : vc1)
        cout << v << " ";
    for(int v : vc2)
        cout << v << " ";
    cout << '\n';
}
void print(int x, int y, int res)
{
    cout << res << '\n';
    go(edge[x].fi, edge[x].se);
    go(edge[y].fi, edge[y].se);
}
void Solve()
{
    while(true)
    {
        shuffle(edge + 1, edge + 2 * n - 2, rng);
        fill(lab, lab + n + 1, -1);
        for(int i=1; i<=n; i++)
            adj[i].clear();
        memset(mark, 0, sizeof mark);
        for(int i=1; i<=2*n-3; i++)
        {
            if(unite(edge[i].fi, edge[i].se))
            {
              //  cout << edge[i].fi << " " << edge[i].se << '\n';
                adj[edge[i].fi].pb(edge[i].se);
                adj[edge[i].se].pb(edge[i].fi);
                mark[i] = 1;
            }
        }
        dfs(1, 0);
        map<int, int> mp;
        for(int i=1; i<=2*n-3; i++)
        {
            if(mark[i]) continue;
            int len = dist(edge[i].fi, edge[i].se) + 1;
            if(mp[len])
            {
                print(mp[len], i, len);
                return;
            }
            mp[len] = i;
        }
    }
}
#define taskname "sol"
int32_t main()
{
    if (fopen(taskname ".inp", "r"))
    {
        freopen(taskname ".inp", "r", stdin);
        //freopen(taskname ".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    //cin >> T;
    for(int itest=1; itest<=T; itest++)
    {
        ReadInput();
        Solve();
    }
}