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#include <iostream>
#include <vector>
#include <queue>
using namespace std;

pair<int, int> bfs(vector<vector<int>>& adj, int start, int n) {
    vector<int> dist(n + 1, -1);
    queue<int> q;
    
    q.push(start);
    dist[start] = 0;
    
    int maxDist = 0;
    int farthestNode = start;
    
    while (!q.empty()) {
        int curr = q.front();
        q.pop();
        
        for (int next : adj[curr]) {
            if (dist[next] == -1) {
                dist[next] = dist[curr] + 1;
                q.push(next);
                
                if (dist[next] > maxDist) {
                    maxDist = dist[next];
                    farthestNode = next;
                }
            }
        }
    }
    
    return {farthestNode, maxDist};
}

int find_max_transfer_time(vector<vector<int>>& adj, int n) {
    pair<int, int> end1 = bfs(adj, 1, n);
    
    pair<int, int> end2 = bfs(adj, end1.first, n);
    
    return end2.second;
}

int main() {
    int n, m;
    cin >> n >> m;
    
    vector<vector<int>> adj(n + 1);
    
    for (int i = 0; i < n-1; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    
    cout << find_max_transfer_time(adj, n) << endl;
    
    return 0;
}