from sys import stdin, stdout
input=stdin.readline

def main():
    N, M = map(int, input().split())
    graph = {}

    for i in range(M):
        A, B = map(int, input().split())
        try:
            graph[A].add(B)
        except:
            graph[A] = {B}
        try:
            graph[B].add(A)
        except:
            graph[B] = {A}
    #print(graph)

    lenCircle=0
    seen = {1:0}



    def depth_search(node, lenCircle):
        for v in graph[node]:
            if v not in seen:
                seen[v] = seen[node]+1
                lenCircle=depth_search(v, lenCircle)
            else:
                lenCircle = max(seen[node]-seen[v]+1, lenCircle)
        return lenCircle

    print(depth_search(1,lenCircle))


main()