Buggy python submission (verdict: Time Limit Exceeded):
# Union Find
class UnionFind():
    # parents:親要素の番号，要素が根なら-グループの要素数
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    # xが所属するグループの根を返す
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    # xとyのグループを併合
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

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

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r))
                         for r in self.roots())

    def max_size_group(self):
        ret = 0
        for mem in self.all_group_members():
            ret = max(ret, len(self.members(mem)))
            # print(self.members(mem))
        return ret


N, M = map(int, input().split())
uf = UnionFind(N)
for i in range(M):
    a, b = map(int, input().split())
    uf.union(a - 1, b - 1)
print(uf.max_size_group())


Fixed submission:
# Union Find
class UnionFind():
    # parents:親要素の番号，要素が根なら-グループの要素数
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    # xが所属するグループの根を返す
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    # xとyのグループを併合
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

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

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r))
                         for r in self.roots())

    # def max_size_group(self):
    #     ret = 0
    #     for mem in self.all_group_members():
    #         ret = max(ret, len(self.members(mem)))
    #         # print(self.members(mem))
    #     return ret


N, M = map(int, input().split())
uf = UnionFind(N)
for i in range(M):
    a, b = map(int, input().split())
    uf.union(a - 1, b - 1)
ans = 0
for i in range(N):
    ans = max(ans, uf.size(i))
print(ans)