arborelantmaxim

#include <bits/stdc++.h>
#define N 100001
using namespace std;
ifstream fin("arborelantmaxim.in");
ofstream fout("arborelantmaxim.out");
int n, Maxim, sol;
int Up[N], Down1[N], Down2[N], Sol[N];
bool Use[N];
vector < pair <int , int> >G[N];
void citire()
{
	fin >> n;
	for(int i=1; i<=n-1; i++)
    {
        int x, y, c;
        fin >> x >> y >> c;
        G[x].push_back(make_pair(y,c));
        G[y].push_back(make_pair(x,c));
	}
}

void DFS1(int Nod)
{
    Use[Nod]=1;
    for(int i=0; i<(int)G[Nod].size(); ++i)
    {
        int Vecin = G[Nod][i].first;
        int Cost = G[Nod][i].second;
        if(!Use[Vecin])
        {
            DFS1(Vecin);
            int Drum = Down1[Vecin] + Cost;
            if(Drum >= Down1[Nod])
            {
                Down2[Nod] = Down1[Nod];
                Down1[Nod] = Drum;
            }
            else
                if(Drum > Down2[Nod])
                    Down2[Nod]=Drum;
        }

    }
}
void DFS2(int Nod)
{
    Use[Nod]=1;
    for(int i=0; i<(int)G[Nod].size(); ++i)
    {
        int Vecin = G[Nod][i].first;
        int Cost = G[Nod][i].second;
        if(!Use[Vecin])
        {
            Up[Vecin] = Up[Nod] + Cost;
            if(Down1[Nod] == (Down1[Vecin] + Cost))
                Up[Vecin] = max(Up[Vecin],Down2[Nod] + Cost);
            else
                Up[Vecin] = max(Up[Vecin],Down1[Nod] + Cost);
            DFS2(Vecin);
        }
    }
    Sol[Nod] = max(Up[Nod],Down1[Nod]);
}
int main()
{
    citire();
    DFS1(1);
    memset(Use,0,sizeof(Use));
    DFS2(1);
    for(int i=1; i<=n; i++)
        if(Sol[i]>Maxim)
            Maxim=Sol[i];
    fout<<Maxim;
    return 0;
}