#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=l; i<=r; i++)
#define IOS {cin.tie(0);cout.tie(0);ios::sync_with_stdio(0);}
using namespace std;

typedef long long ll;
typedef pair<int,int> P;
const int N = 510;

vector <int> e[N], ans[N];

int sz[N], son[N], vis[N], mnsz, mxd;

void dfs(int u, int ff) {
    sz[u] = 1;
    son[u] = 0;
    // vis[u] = 1;
    for (auto v: e[u]) {
        if (vis[v] || v == ff) continue;
        dfs(v, u);
        sz[u] += sz[v];
        if (sz[v] > sz[son[u]]) son[u] = v;
    }
}

void divide(int u, int d) {
    mxd = max(mxd, d);
    dfs(u, 0);
    int rt = u, tot = sz[u];
	while (sz[son[rt]]*2 > tot) rt = son[rt];
    vis[rt] = 1;
    ans[d].push_back(rt);
    for (auto v: e[rt]) {
        if (!vis[v]) {
            divide(v, d+1);
        }
    }
}

int main() {
    int n; scanf("%d", &n);
    rep (i, 1, n-1) {
        int u, v; scanf("%d%d", &u, &v);
        e[u].push_back(v);
        e[v].push_back(u);
    }
    divide(1, 0);
    cout << mxd<<endl;
    for (int i = mxd; i >= 0; i--) {
        int len = ans[i].size();
        cout << len<<' ';
        rep (j, 0, len-1) {
            cout << ans[i][j]<<' ';
        }
        cout <<'\n';
    }
    return 0;
}