import sys
input=sys.stdin.readline
sys.setrecursionlimit(10**6)

from math import gcd

def solv():
 N,M=map(int,input().split())
 graph=[[] for _ in range(N+1)]
 for i in range(M):
  A,B=map(int,input().split())
  graph[A].append(B)
  graph[B].append(A)

 res=0  
 level={1:0}

 def dfs(v,res):
  for w in graph[v]:
   if w not in level:
    level[w]=level[v]+1
    res=dfs(w,res)
   else:
    res=max(res,level[v]-level[w]+1)
  return res

 res=dfs(1,res)
 print(res)

solv()