#include <iostream>
#include <vector>
#include <stack>
#include <queue>
#include <fstream>
#include <stdlib.h>
#include <time.h>
using namespace std;

ifstream f("darb.in");
ifstream g("darb.out");

int n,m,mx,nmx,nmx2,mid;
vector<vector<long long int> >graph;
vector<int>visited;
vector<int> parc;
stack<int>lant_max;

void bfs(int vertex)
{if(vertex<0||vertex>n-1)
    return;
queue<int> q;
unsigned int element,i;
q.push(vertex);
visited[vertex]++;
while(!q.empty())
    {element=q.front();
    for(i=0;i<graph[element].size();i++)
        if(visited[graph[element][i]]==-1)
            {q.push(graph[element][i]);
            visited[graph[element][i]]=visited[element]+1;
            parc[graph[element][i]]=element;
            }
    q.pop();
    }
}


int main()
{f>>n>>m;
graph.resize(n);
visited.resize(n,-1);
parc.resize(n,-1);
int x,y,i;
for(i=0;i<m;i++)
    {
    f>>x>>y;
    x--;
    y--;
    graph[x].push_back(y);
    graph[y].push_back(x);
    }
srand(time(NULL));
x=rand()%n;
bfs(x);

mx=-1;
for(i=0;i<n;i++)
    {if(visited[i]>mx)
        {mx=visited[i];
        nmx=i;
        }
    }

for(i=0;i<n;i++)
    visited[i]=-1;
for(i=0;i<n;i++)
    parc[i]=-1;

bfs(nmx);
mx=-1;
for(i=0;i<n;i++)
    {if(visited[i]>mx)
        {mx=visited[i];
        nmx2=i;
        }
    }

g<<mx+1;

return 0;
}