#include<bits/stdc++.h>
using namespace std;
const int N = 1505;
vector<int> e[N];
vector<int>a;
int siz[N], root, mx = 1e9, del[N] = { 0 }, p = 0;
vector<int> ans[20];
void getroot(int u, int fa, int tot) {
	siz[u] = 1;
	int ms = 0;
	for (auto& v : e[u]) {
		if (v == fa || del[v])continue;
		getroot(v, u, tot);
		siz[u] += siz[v];
		ms = max(ms, siz[v]);
	}
	ms = max(ms, tot - siz[u]);
	if (ms < mx)root = u, mx = ms;
}
void dfs(int u, int fa,int m) {
	p = max(p, m);
	mx = 1e9;
	getroot(u, 0, siz[u]);
	u = root;
	getroot(u, 0, siz[u]);
	del[u] = 1;
	ans[m].push_back(u);
	for (auto& v : e[u]) {
		if (del[v] || v == fa)continue;
		dfs(v, 0, m + 1);
	}
}
void solve() {
	int n;
	cin >> n;
	for (int i = 1; i < n; i++) {
		int u, v;
		cin >> u >> v;
		e[u].push_back(v);
		e[v].push_back(u);
	}
	siz[1] = n;
	dfs(1, 0, 0);
	cout << p+1 << '\n';
	for (int i = p; i >=0;i--) {
		cout << ans[i].size() << ' ';
		for (auto& v : ans[i])cout << v << ' ';
		cout << '\n';
	}
}
int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	//int t;
	//cin >> t;
	//while (t--)
	solve();

	return 0;
}