#include <bits/stdc++.h>
using namespace std;
typedef  long long int ll;
#define INF LLONG_MAX

vector<ll> dist(100005,INF);
vector<bool> visited(100005,false);
vector<bool> p(100005,false);
ll n,m,a,b,c;
vector<ll> adj[100005];
vector<ll> g[100005];

void dfs(ll s , ll q){

    if(p[s] == true) return;
    p[s] = true;
    g[q].push_back(s);
    for(auto u : adj[s]) dfs(u,q);
}

void dijkstra(ll s){

    for(ll i = 0; i < n; i++){
        dist[i] = INF;
        visited[i] = false;
    }

    priority_queue<pair<ll,ll>> q;

    dist[s] = 0;
    q.push({0,s});

    while(!q.empty()){

        ll a = q.top().second;
        q.pop();

        if(visited[a] == true) continue;
        visited[a] = true;

        for(auto u : adj[a]){

            if(dist[a] + 1 < dist[u]){

                dist[u] = dist[a]+1;
                q.push(make_pair(-dist[u],u));
            }
        }
    }
}
int main() {

   cin >> n >> m;
   vector<ll> outdegree(n+5);

    for(ll i = 0; i < m; i++){

       cin >> a >> b;
       outdegree[a-1]++;
       outdegree[b-1]++;
       adj[a-1].push_back(b-1);
       adj[b-1].push_back(a-1);
   }

    ll total = -INF;

    ll c = 0;
    for(ll i = 0; i < n; i++){

        if(p[i] == true) continue;
        g[c].push_back(i);
        dfs(i,c);
        c++;
    }

    for(ll y = 0; y < c; y++) {

        ll best = 0;
        ll node;

        for(auto z : g[y]){

            if(outdegree[z] > best){
                node = z;
                best = outdegree[z];
            }
        }

        dijkstra(node);

        for (ll i = 0; i < n; i++) {
            if(dist[i] != INF){
                total = max(total, dist[i]);
            }
        }

    }

   cout << total;

    return 0;
}