DiamterOfTree

#include <bits/stdc++.h>

using namespace std;

struct Node{
    vector<int> links;
    int depth;
};

int n;
vector<Node> tree;
vector<bool> visited;
int mxd;
int mxn;

void findDepth(int node){
    visited[node] = true;
    //cout << node << ", " << tree[node].depth << '\n';
    //cout << tree[node].depth << '\n';
    for(auto v: tree[node].links){
        if(!visited[v]){
            tree[v].depth = tree[node].depth+1;
            if(tree[v].depth>mxd){
                mxd = tree[v].depth;
                mxn = v;
            }
            findDepth(v);
        }
    }
}

int main(){
    //freopen("diameter.in", "r", stdin);

    cin >> n;
    tree.resize(n+1);
    visited.resize(n+1);
    int a, b;
    while(cin >> a){
        cin >> b;
        tree[a].links.push_back(b);
        tree[b].links.push_back(a);
    }
    findDepth(1);
    fill(visited.begin(), visited.end(), false);
    //cout << "==========" << '\n';
    mxd = 0;
    tree[mxn].depth = 0;
    findDepth(mxn);
    cout << mxd << '\n';

    return 0;
}