#include <iostream>
#include <vector>
using namespace std;
vector<vector<int>> adj;
vector<int> reteg;
vector<bool> vis;
int ans;

void dfs(int s,int parent)
{
vis[s]=true;
reteg[s]=reteg[parent]+1;
for(int x:adj[s])
    {
    if(!vis[x])dfs(x,s);
    else ans=max(ans,reteg[x]-reteg[s]+1);
    }
}


int main()
{
    int n,m;
    cin>>n>>m;
    ans=0;
    adj.resize(n+1);
    vis.resize(n+1);
    reteg.resize(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);
        }
    reteg[0]=-1;
    dfs(1,0);
    cout<<ans;
    return 0;
}