#line 1 "test/GRL_5_A.test.cpp"
#define PROBLEM "https://onlinejudge.u-aizu.ac.jp/courses/library/5/GRL/5/GRL_5_A"
#line 1 "macro/macros.hpp"



/*
@title Macro
@category template
*/
#include <bits/stdc++.h>
using namespace std;
#define rep(i,N) for(int i=0;i<int(N);++i)
#define rep1(i,N) for(int i=1;i<int(N);++i)
#define all(a) (a).begin(),(a).end()
#define print(v) { cerr<<#v<<": [ "; for(auto _ : v) cerr<<_<<", "; cerr<<"]"<<endl; }
#define printpair(v) { cerr<<#v<<": [ "; for(auto _ : v) cerr<<"{"<<_.first<<","<<_.second<<"}"<<", "; cerr<<"]"<<endl; }
#define dump(x) cerr<<#x<<": "<<x<<endl;
#define bit(k) (1LL<<(k))
#define Yes "Yes"
#define No "No"
#define YES "YES"
#define NO "NO"
typedef long long ll;

template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 >& p) {
  os << "{" <<p.first << ", " << p.second << "}";
  return os;
}
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

const int INF = (ll)1e9;
const ll INFLL = (ll)1e18+1;
const ll MOD = (ll)1e9+7;

const double PI = acos(-1.0);

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const string dir = "DRUL";


#line 1 "tree/template.cpp"


#line 1 "graph/template.hpp"


#line 4 "graph/template.hpp"

/*
@title Graph Class
@category template
*/
template<typename T = int>
struct edge{
    int to;
    T cost;
    int id;
    edge(int _to, T _cost = 1, int _id = -1) :to(_to), cost(_cost), id(_id) {}
};

template<class T>
class Graph {
  public:
    int N;
    vvec<edge<T>> G;
    Graph(int _N): N(_N),G(_N){
    }
    void add_Directed_edge(int from, int to, T cost = 1, int id = -1){
        G[from].push_back({to, cost, id});
    }
    void add_edge(int v1, int v2, T cost = 1, int id = -1){
        add_Directed_edge(v1, v2, cost, id);
        add_Directed_edge(v2, v1, cost, id);
    }
    //standard input
    void input(int M, int padding = -1, bool weighted = false, bool directed = false){
        while(M--){
            int a, b;
            cin >> a >> b;
            a += padding;
            b += padding;
            T c = T(1);
            if(weighted)cin >> c;
            if(directed)add_Directed_edge(a,b,c);
            else add_edge(a,b,c);
        }
    }
};

#line 5 "tree/template.cpp"

/*
@title Tree Class
@category template
*/
template<class T>
class Tree {
  public:
    int N;
    vvec<edge<T>> G;
    Tree(int _N): N(_N),G(_N){
    }
    void add_Directed_edge(int from, int to, T cost = 1, int id = -1){
        G[from].push_back({to, cost, id});
    }
    void add_edge(int v1, int v2, T cost = 1, int id = -1){
        add_Directed_edge(v1, v2, cost, id);
        add_Directed_edge(v2, v1, cost, id);
    }
    //standard input
    void input(int M, int padding = -1, bool weighted = false, bool directed = false){
        while(M--){
            int a, b;
            cin >> a >> b;
            a += padding;
            b += padding;
            T c = T(1);
            if(weighted)cin >> c;
            if(directed)add_Directed_edge(a,b,c);
            else add_edge(a,b,c);
        }
    }
};


#line 1 "tree/tree-diameter.cpp"
/*
@title 木の直径/Diameter of a Tree (全方位木DP/Rerooting ver.)
@category tree
*/
#line 7 "tree/tree-diameter.cpp"

template<typename T>
class Diameter :  public Tree<T>{
  public:
    using Tree<T>::N;
    using Tree<T>::G;
    vector<T> d;
    vector<T> ans;
    T diameter;
    Diameter(int _N):Tree<T>::Tree(_N), d(_N,0), ans(_N){}
    //Calc distance and start Rerooting
    void build(int start = 0, int pre = -1, bool debug = false){
        dfs1(start, pre);
        dfs2(start, pre);
        if(debug){
            print(d);
            print(ans);
        }
        diameter = *max_element(ans.begin(), ans.end());
    }
    //calculate the distance from start
    void dfs1(int cur = 0, int pre = -1){
        d[cur] = 0;
        for(edge<T>& ne: G[cur]){
            if(ne.to == pre)continue;
            dfs1(ne.to, cur);
            d[cur] = max(d[cur],d[ne.to] + ne.cost);
        }
    }
    void dfs2(int cur = 0, int pre = -1, T d_par = 0){
        //rerooting
        vector<pair<T,int>> childs;
        childs.push_back({0, -1}); //番兵 次数が1だと壊れるので
        for(auto ne: G[cur]){
            if(ne.to == pre)childs.push_back({d_par + ne.cost, ne.to});
            else childs.push_back({d[ne.to] + ne.cost, ne.to});
        }
        sort(all(childs), greater<pair<T, int>>());
        //大きい二つ
        ans[cur] = childs[0].first + childs[1].first;
        for(auto ne: G[cur]){
            if(ne.to == pre)continue;
            //降りる辺が最大値
            if(childs[0].second == ne.to)
                dfs2(ne.to, cur, childs[1].first);
            else 
                dfs2(ne.to, cur, childs[0].first);
        }
    }
    T get_diameter(){
        return diameter;
    }
};
#line 5 "test/GRL_5_A.test.cpp"


int main(){
    int N;
    cin >> N;
    Diameter<long long> G(N);
    G.input(N-1, 0, true, false);
    G.build(N/2);
    cout << G.get_diameter() << endl;
}



Measured memory_bytes: 20884