#include <bits/stdc++.h>
using namespace std;

#define int long long

vector<vector<int>> adj;
vector<int> vis;
int maxi = 0;

void dfs(int v, int p) {
    for (int u : adj[v]) {
        if (u==p)continue;
        if (vis[u]>0) {
            maxi=max(maxi,vis[v]-vis[u]+1);
        } else {
            vis[u]=vis[v]+1;
            dfs(u, v);
        }
    }
}

signed main() {
	int n, m;
    cin >> n >> m;
    adj.resize(n+1);
    vis.resize(n+1);
    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    for (int i = 1; i <= n; i++) {
        if (vis[i]==0) {
            vis[i]=1;
            dfs(i, 0);
        }
    }
    cout<<maxi;
}