#include <bits/stdc++.h>

using namespace std;

ifstream f("darb.in");
ofstream g("darb.out");



class graf
{                       /// prea multi in clasa
                        /// orientat != tipul clasei
    int nr_noduri, nr_muchii, orientat;

    vector<vector<int>> lista_muchii;
    vector<vector<int>>  lista_muchii_transpusa;
    vector<vector<int>> CTC;
    vector<int> havel;
    vector<vector<pair<int, int>>> lista_cu_costuri;
    vector<int> ind;
    vector<int> gr;

    int matrice[101][101];

    void dfs1(int nod, int nr, vector<bool> &vizitat, int &maxx, int &x);
    void DFSx(int nod, vector<int>&v);
    void DFS_TR(int nod,vector<int> &vizitat, int nr);
    void DFS_CTC(int nod, vector<int> &vizitat, stack<int> &st);
    void dfs_mic(int x, vector<bool> &vizitat, stack<int>&stiva);
public:

    graf();

    graf(int nr_noduri, int nr_muchii, int orientat);

    ~graf() {}

    void BFS(int start);
    void DFS(int start);
    void CTCC();
    void TOPO();
    void APM();
    void HH();
    void RF();
    void diametru();
};

graf::graf(){
    nr_noduri = 0;
    nr_muchii = 0;
    orientat = 0;
}

graf::graf(int nr_noduri, int nr_muchii, int orientat){

    if(orientat < 2)
    {
        int i = 0, nod1, nod2;

        lista_muchii.resize(nr_noduri+1);

        this->nr_noduri = nr_noduri;
        this->nr_muchii = nr_muchii;
        this->orientat = orientat;

        while(i < nr_muchii)
        {
            f>>nod1>>nod2;
            if(orientat)
                lista_muchii[nod1].push_back(nod2);
            else
            {
                lista_muchii[nod1].push_back(nod2);
                lista_muchii[nod2].push_back(nod1);
            }
            i++;
        }
    }
    else if(orientat == 2)
    {
        int x;
        havel.clear();
        while(f >> x)
            havel.push_back(x);
    }
    else if(orientat > 2 && orientat < 10)
    {
        this->nr_noduri = nr_noduri;
        this->nr_muchii = nr_muchii;
        lista_muchii.clear();
        CTC.clear();
        lista_muchii.resize(nr_noduri+1);
        int i, x, y;
        for(i = 1; i <= nr_muchii; i++)
        {
            f>>x>>y;
            lista_muchii[x].push_back(y);
            lista_muchii_transpusa[y].push_back(x);
        }
    }
    else if(orientat == 10)
    {
        lista_cu_costuri.clear();
        lista_cu_costuri.resize(nr_noduri + 1);

        int i, nod1, nod2, cost;
        this->nr_noduri = nr_noduri;
        this->nr_muchii = nr_muchii;
        pair<int,int> aux;
        for(i = 1; i <= nr_muchii; i++)
        {
            f>>nod1>>nod2>>cost;
            aux.first = nod2;
            aux.second = cost;
            lista_cu_costuri[nod1].push_back(aux);
            aux.first = nod1;
            lista_cu_costuri[nod2].push_back(aux);
        }
    }
    else if(orientat == 11)
    {
        this->nr_noduri = nr_noduri;
        int i, j;
        for(i = 1; i <= nr_noduri; i++)
            for(j = 1; j <= nr_noduri; j++)
                f>>matrice[i][j];
    }
}

///----------------------------------------------------------------------------------bfs
void graf::BFS(int inceput){
    int i = 0, nod_curent;

    queue<int> q;

    vector<int>vizitat;
    vector<int>distanta;

    q.push(inceput);

    do
    {
        vizitat.push_back(0);
        distanta.push_back(-1);
        i++;

    }
    while(i <= nr_noduri);

    vizitat[inceput] = 1;
    distanta[inceput] = 0;

    while(!q.empty())
    {
        nod_curent = q.front();
        q.pop();
        for (auto j = lista_muchii[nod_curent].begin(); j != lista_muchii[nod_curent].end(); j++)
            if(!vizitat[*j])
            {
                vizitat[*j] = 1;
                q.push(*j);
                distanta[*j] = distanta[nod_curent] + 1;
            }
    }
    int marime = distanta.size();
    for(i = 1; i < marime; i++)
        g<<distanta[i]<<" ";
}
///----------------------------------------------------------------------------------DFS

void graf::DFSx(int start, vector<int> &vizitat){
    vizitat[start] = 1;
    auto jos = lista_muchii[start].begin();
    auto sus = lista_muchii[start].end();
    auto j = jos;
    while(j != sus)
    {
        if(vizitat[*j] == 0)
            DFSx(*j, vizitat);
        j++;
    }
}

void graf::DFS(int start){

    int i = 0, nr_componente_conexe = 0,  marime;

    vector<int> vizitat;
    do
    {
        vizitat.push_back(0);
        i++;

    }
    while(i <= nr_noduri);

    marime = vizitat.size();

    for(i = 1; i < marime; i++)
        if(vizitat[i] == 0)
        {
            DFSx(i,vizitat);
            nr_componente_conexe++;
        }
    g<<nr_componente_conexe;
}
///----------------------------------------------------------------------------------HH

void graf::HH(){
    int i, ok = 1;
    do
    {
        sort(havel.begin(), havel.end(),greater<int>());

        if(havel[0] == 0)
            break;

        int x = havel[0];
        havel.erase(havel.begin());

        if(x > havel.size())
            ok = 0;

        for(i = 0; i < x && ok == 1; i++)
        {
            havel[i]--;
            if(havel[i] < 0)
                ok  = 0;
        }

    }
    while(ok);
    if(ok == 0)
        g<<"NU";
    else
        g<<"DA";
}



///------------------------------------------------------------------------------TOPOLOGICA
void graf::dfs_mic(int x, vector<bool>&vizitat, stack<int> &stiva){
    vizitat[x] = 1;
    int marime = lista_muchii[x].size(), i = 0;
    while(i < marime)
    {
        if(vizitat[lista_muchii[x][i]] == 0)
            dfs_mic(lista_muchii[x][i], vizitat, stiva);
        i++;
    }
    stiva.push(x);

}

void graf::TOPO(){
    stack <int> stiva;
    vector<bool> vizitat;
    int i = 0;

    do
    {
        vizitat.push_back(0);
        i++;
    }
    while(i <= nr_noduri + 1);

    for(i = 1; i <= nr_noduri; i++)
        if(vizitat[i] == 0)
            dfs_mic(i, vizitat, stiva);
    while(stiva.empty() == 0)
    {
        g<<stiva.top()<<" ";
        stiva.pop();
    }
}

///------------------------------------------------------------------------CTC
/*
void graf::DFS_CTC(int nod, vector<int>&vizitat, stack<int> &st){
    int i = 0, urm;
    vizitat[nod] = 1;
    int marime;
    marime = lista_muchii[nod].size();
    for(i = 0; i < marime; i++)
    {
        urm = lista_muchii[nod][i];
        if(!vizitat[urm])
            DFS_CTC(urm, vizitat, st);
    }
    st.push(nod);
}
void graf::DFS_TR(int nod, vector<int> &vizitat, int nr){
    int i, urm;
    vizitat[nod] = 2;
    CTC[nr].push_back(nod);
    int marime = lista_muchii_transpusa[nod].size();
    for(i = 0; i < marime; i++)
        {urm = lista_muchii_transpusa[nod][i];
    if(vizitat[urm] == 1)
        DFS_TR(urm, vizitat, nr);
}
}
void graf::CTCC(){
    int i = 0,nod, nr = 0;
    stack<int> st;
    while(!st.empty())
        st.pop();
    vector<int> vizitat;
    do
    {
        vizitat.push_back(0);
        i++;
    }
    while(i <= nr_noduri);
    for(i = 1; i <= nr_noduri; i++)
        if(vizitat[i] == 0)
            DFS_CTC(i,vizitat, st);
    while(!st.empty())
    {
        int nod = st.top();
        if(vizitat[nod] == 1)
        {
            nr++;
            DFS_TR(nod, vizitat, nr);
        }
        st.pop();
    }
    g<<nr<<"\n";
    for(i = 1; i <= nr; i++)
        for(int j = 0; j < CTC[i].size(); j++)
            g<<CTC[i][j]<<" ";
        g<<"\n";
}
*/
///----------------------------------------------------------------------APM
void graf::APM(){
    int i = 0, urm, nod, j;
    int minn = INT_MAX, minni;

    vector <int> parinte;
    vector <int> situatie;
    vector <int> vizitat;

    do
    {
        situatie.push_back(INT_MAX);
        vizitat.push_back(0);
        parinte.push_back(0);
        i++;
    }
    while(i <= nr_noduri + 1);

    situatie[1] = 0;
    parinte[1] = -1;

    for(i = 1; i <= nr_noduri; i++)
    {
        minn = INT_MAX;
        for(nod = 1; nod <= nr_noduri; nod++)
            if(vizitat[nod] == 0)
                if(situatie[nod] < minn)
                {
                    minn = situatie[nod];
                    minni = nod;
                }
        vizitat[minni] = 1;

        int marime = lista_cu_costuri[minni].size();

        for(j = 0; j < marime; j++)
            if(vizitat[lista_cu_costuri[minni][j].first] == 0 && lista_cu_costuri[minni][j].second < situatie[lista_cu_costuri[minni][j].first])
            {
                parinte[lista_cu_costuri[minni][j].first] = minni;
                situatie[lista_cu_costuri[minni][j].first] = lista_cu_costuri[minni][j].second;

            }
    }
    int cost_total = 0;

    for(i = 1; i <= nr_noduri; i++)
        cost_total += situatie[i];

    g<<cost_total<<"\n"<<nr_noduri - 1 <<"\n";
    for(i = 2; i <= nr_noduri; i++)
        g<<parinte[i]<<" "<<i<<"\n";

}
///----------------------------------------------------------------------ROY FLOYD
void graf::RF()
{
    int i, j, k;

    for(i = 1; i <= nr_noduri; i++)
        for(j = 1; j <= nr_noduri; j++)
            for(k = 1; k <= nr_noduri; k++)
                if(matrice[j][i] && matrice[i][k] && (matrice[j][k] > matrice[j][i] + matrice[i][k] || !matrice[j][k]) && j != k )
                    matrice[j][k] = matrice[j][i] + matrice[i][k];

    for(i = 1; i <= nr_noduri; i++)
        {for(j = 1; j <= nr_noduri; j++)
            g<<matrice[i][j]<<" ";
            g<<"\n";}
}
///----------------------------------------------------------------------Diametru
void graf::dfs1(int nod, int nr, vector<bool> &vizitat, int &maxx, int &x)
{
    vizitat[nod] = 1;
    nr++;
    for(auto j = lista_muchii[nod].begin(); j != lista_muchii[nod].end(); j++)
        if(vizitat[*j] == 0)
            {
                if(nr >= maxx)
                {
                    maxx = nr;
                    x = *j;
                }
                dfs1(*j, nr, vizitat, maxx, x);
            }
}
void graf::diametru()
{
    vector<bool> vizitat;
    vector<bool> vizitat2;
    int nr = 0, maxx = INT_MIN, x = 0, i = 0;

    for(i = 0; i <= nr_noduri; i++)
        vizitat.push_back(0);
    dfs1(1, nr + 1, vizitat, maxx, x);


    nr = 0;

    for(i = 0; i <= nr_noduri; i++)
        vizitat2.push_back(0);
    dfs1(x, nr + 1, vizitat2, maxx, x);

    g<<maxx;


}


int main(){
    int n, m, s;
    f>>n;
    //--------------------|
    //graf test(n,m,0);   |
    //test.DFS(1);        |DFS
    //--------------------|
    //--------------------|
    //graf test(n,m,1);   |
    //test.TOPO();        |TOPO
    //--------------------|
    //--------------------|
    //graf test(0,0,2);   |HH
    //test.HH();          |
    //--------------------|
    //--------------------|
    //graf test(n, m, 3); |
    //test.CTCC();        |CTC
    //--------------------|
    //--------------------|
    //graf test(n, m, 10);|
    //test.APM();         |APM
    //--------------------|
    //--------------------|
    //graf test(n, 0, 11);|ROY FLOYD
    //test.RF();          |
    //--------------------|

    graf test(n, n - 1, 0);
    test.diametru();

    return 0;
}