class unionfind:
    def __init__(self,uni_num):
        self.uni_num=uni_num
        self.union_root = [-1 for i in range(self.uni_num + 1)]
        self.union_depth = [0] * (self.uni_num + 1)
        self.e_num=[0]*(self.uni_num+1)

    def find(self,x):  # 親は誰？
        if self.union_root[x] < 0:
            return x
        else:
            self.union_root[x] = self.find(self.union_root[x])
            return self.union_root[x]

    def unite(self,x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            self.e_num[x]+=1
            return
        if self.union_depth[x] < self.union_depth[y]:
            x, y = y, x
        if self.union_depth[x] == self.union_depth[y]:
            self.union_depth[x] += 1
        self.union_root[x] += self.union_root[y]
        self.union_root[y] = x
        self.e_num[x]=max(self.e_num[x],self.e_num[y])+1


    def size(self,x):
        return -self.union_root[self.find(x)]

    def same(self,x,y):
        return self.find(x)==self.find(y)
    def edge(self,x):
        return self.e_num[self.find(x)]


n,m=map(int,input().split())
uf=unionfind(n+2)
e=[]
for i in range(m):
    u,v=map(int,input().split())
    e.append((u,v))
e.reverse()
for u,v in e:uf.unite(u,v)
print(uf.edge(1))