#include <bits/stdc++.h>

using namespace std;

ifstream fin("dmax.in");
ofstream fout("dmax.out");

int n, m, x, y,q[101],d[1001],a[1001][1001],nod,viz[101];

void Citire()
{
    fin >> n >> m;
    while(fin >> x >> y)
    {
        a[x][y] =  a[y][x] = 1;
    }
}

void BFS(int S)
{ int i;
   int pr,ul;
   pr = ul = 1;
   viz[S] = 0;
   q[1] = S;
   d[S] = 0;
   while(pr <= ul)
   {
       nod=q[pr];
       pr++;
       for( i = 1;i <= n;i++)
        if(viz[i] == 0 && a[nod][i] == 1)
       {
           viz[i] = 1;
           q[++ul] = i;
           d[i] = 1 +d[nod];
       }
   }
}

int main()
{ int maxim, i;
   Citire();
   BFS(1);
   maxim=0;
   for(i = 1;i <= n; i++)
    if(d[i] > maxim) maxim =d[i];
    fout << maxim;
   fin.close();
   fout.close();
    return 0;
}