#include <stdio.h>
#include<string.h>
#define NMAX 100000
using namespace std;

int n,use[NMAX],c[NMAX],D[NMAX],nr,mx,i;

struct lista
{
    int nod;
    lista *urm;
}*g[NMAX];

void adauga (int i,int j)
{
    lista *aux=new lista;
    aux->nod=i;
    aux->urm=g[j];
    g[j]=aux;
}

void bf(int start)
{
    lista *p;
    memset(use,0,sizeof(use));
    use[start]=1;
    int nod,st,dr;
    st=dr=1;
    c[st]=start;
    for(D[start]=0;st<=dr;st++)
    {
        nod=c[st];
        for(p=g[nod];p;p=p->urm)
            if(!use[p->nod])
        {
            use[c[++dr]=p->nod]=1;
            D[p->nod]=D[nod]+1;
            if(D[p->nod]>mx){mx=D[p->nod];nr=p->nod;}
        }
    }


}
 FILE *f1=fopen("darb.in","r"),*f2=fopen("darb.out","w");
 int m;
int main()
{

  fscanf(f1,"%d%d",&n,&m);
  for(i=1;i<=m;i++)
  {int x,y;fscanf(f1,"%d%d",&x,&y);adauga(x,y);adauga(y,x);}
  bf(1);
  bf(nr);
  fprintf(f2,"%d",mx+1);
  return 0;
}

//Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time.