// Kaktuszgráf.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <vector>
using namespace std;
void dfs(vector<vector<int>>& adj, int& maxi, int i, vector<int>& dist)
{
    for (auto next : adj[i])
    {
        if (dist[next] == -1)
        {
            dist[next] = dist[i] + 1;
            dfs(adj, maxi, next, dist);
        }
        else if(next!=i)
        {
            if (dist[i] - dist[next] + 1 > maxi)
                maxi = dist[i] - dist[next]+1;
        }
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    vector<vector<int>> adj(n + 1);
    for (int i = 0; i < m; i++)
    {
        int x, y;
        cin >> x >> y;
        adj[x].push_back(y);
        adj[y].push_back(x);
    }
    int maxi = 0;
    vector<int>dist(n + 1, -1);
    dist[1] = 0;
    dfs(adj, maxi, 1,dist);
    cout << maxi;
}

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