//無向グラフの木の直径を求める(重みなしなら辺のcostを1に)
struct edge
{
    long long to;
    long long cost;
    edge(long long t, long long c) : to(t), cost(c) {}
};
pair<long long, long long> dia_dfs(const vector<vector<edge>> &G, long long v, long long par)
{
    pair<long long, long long> ret = make_pair(0, v);
    for (auto e : G[v])
    {
        long long nv = e.to;
        if (nv == par)
            continue;
        auto next = dia_dfs(G, nv, v);
        next.first += e.cost;
        ret = max(ret, next);
    }
    return ret;
}
long long tree_diameter(const vector<vector<edge>> &G)
{
    auto p = dia_dfs(G, 0, -1), q = dia_dfs(G, p.second, -1);
    return q.first;
}
//木の直径の端点の組の1つを返す(0-indexed)
pair<long long, long long> tree_end_nodes(const vector<vector<edge>> &G)
{
    auto p = dia_dfs(G, 0, -1), q = dia_dfs(G, p.second, -1);
    return make_pair(p.second, q.second);
}