#include <bits/stdc++.h>
using namespace std;

// 5
// 1 2
// 4 1
// 2 3
// 3 4
// 5 3
// 5 2
// 5 4

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

	int n;
	cin >> n;
	vector<vector<int>> adj(n + 1);
	vector<int> deg(n + 1);
	for (int i = 0; i < (2 * n - 3); i++) {
		int u, v;
		cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	for (int i = 1; i <= n; i++) {
		deg[i] = adj[i].size();
	}

	vector<int> cc;
	vector<int> vis(n + 1);

	const function<void(int)> ff = [&](int v) -> void {
		for (auto c : adj[v]) {
			if (vis[c] > 0) continue;
			vis[c]++;
			cc.push_back(c);
			ff(c);
		}
	};

	const int B = 20;
	vector<vector<int>> up(n + 1, vector<int>(B + 1));
	vector<int> dep(n + 1);

	auto lca = [&](int p, int q) -> int {
		int dp = dep[p], dq = dep[q];
		if (dp < dq) {
			swap(p, q);
			swap(dp, dq);
		}
		int need = dp - dq;
		for (int i = B; i >= 0; i--) {
			if (need >= (1 << i)) {
				need -= (1 << i);
				p = up[p][i];
			}
		}
		if (p == q) return p;
		for (int i = B; i >= 0; i--) {
			int a = up[p][i], b = up[q][i];
			if (a != b) {
				p = a, q = b;
			}
		}
		return up[p][0];
	};

	auto get_distance = [&](int p, int q) -> int {
		return dep[p] + dep[q] - 2 * dep[lca(p, q)];
	};

	auto print_cycle = [&](int x, int y) -> void {
		int L = lca(x, y);
		vector<int> xx, yy;  
		int cur_x = x, cur_y = y;
		while (cur_x != L) {
			xx.push_back(cur_x);
			cur_x = up[cur_x][0];
		}
		while (cur_y != L) {
			yy.push_back(cur_y);
			cur_y = up[cur_y][0];
		}
		for (int i = 0; i < (int)xx.size(); i++) {
			cout << xx[i] << ' ';
		}
		cout << L << ' ';
		for (int i = (int)yy.size() - 1; i >= 0; i--) {
			cout << yy[i] << ' ';
		}
		cout << '\n';
	};

	map<int, set<pair<int, int>>> cyc;

	vector<vector<int>> triangles;
	for (int i = 1; i <= n; i++) {
		if (vis[i] > 0) continue;
		cyc.clear();
		cc.clear();
		cc.push_back(i);
		vis[i]++;
		ff(i);
		int sz = cc.size();
		int cnt_edges = 0;
		for (auto c : cc) {
			cnt_edges += deg[c];
		}
		cnt_edges /= 2;
		if (sz <= 2) continue;
		else if (sz == 3) {
			if (cnt_edges <= 2) continue;
			triangles.push_back(cc);
			if (triangles.size() >= 2) {
				// cerr << "triangles " << '\n';
				cout << 3 << '\n';
				for (int j = 0; j < 2; j++) {
					for (int k = 0; k < 3; k++) {
						cout << triangles[j][k] << ' ';
					}
					cout << '\n';
				}
				return 0;
			}
		} else if (sz >= 4) {
			if (cnt_edges < 2 * sz - 3) {
				continue;
			}
			int root = -1;
			for (auto c : cc) {
				if (deg[c] >= 3) {
					root = c;
					break;
				}
			}
			assert(root != -1);
			vis[root]++;
			queue<int> Q;
			Q.push(root);
			
			while (!Q.empty()) {
				int v = Q.front();
				Q.pop();
				for (auto c : adj[v]) {
					if (c == up[v][0]) continue;
					if (vis[c] >= 2) {
						//v ke c udah ada
						int dis = get_distance(c, v);
						if (cyc[dis + 1].count(make_pair(min(c, v), max(c, v)))) continue;
						cyc[dis + 1].emplace(make_pair(min(c, v), max(c, v)));
						if (cyc[dis + 1].size() >= 2) {
							cout << dis + 1 << '\n';
							for (auto ccc : cyc[dis + 1]) {
								// cerr << cyc[dis + 1][i].first << ' ' << cyc[dis + 1][i].second << '\n';
								print_cycle(ccc.first, ccc.second);
							}
							return 0;
						} 
						continue;
					}
					dep[c] = dep[v] + 1;
					vis[c]++;
					up[c][0] = v;
					for (int i = 1; i <= B; i++) {
						up[c][i] = up[up[c][i - 1]][i - 1];
					}
					Q.push(c);
				}
			}
			return 0;
		}
	}
	assert(false);
}