output_description: Print the answer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N M
      A_1 B_1
      \vdots
      A_M B_M
attempt: import sys
  from io import StringIO
  import unittest
  
  
  def resolve():
      N, M = map(int, input().split())
      l = []
      for _ in range(M):
          i, j = map(int, input().split())
          gi = find_group(l, i)
          if not gi:
              gi = {i}
              l.append(gi)
          gj = find_group(l, j)
          if not gj:
              gj = {j}
              l.append(gj)
          l.remove(gi)
          if gi != gj:
              l.remove(gj)
          gi = gi | gj
          l.append(gi)
      max_size = 0
      for s in l:
          max_size = max(max_size, len(s))
      print(max_size)
  
  
  def find_group(l, i):
      for s in l:
          if i in s:
              return s
      return None
  
  
  class TestClass(unittest.TestCase):
      def assertIO(self, input, output):
          stdout, stdin = sys.stdout, sys.stdin
          sys.stdout, sys.stdin = StringIO(), StringIO(input)
          resolve()
          sys.stdout.seek(0)
          out = sys.stdout.read()[:-1]
          sys.stdout, sys.stdin = stdout, stdin
          self.assertEqual(out, output)
  
      def test_入力例_1(self):
          input = """5 3
  1 2
  3 4
  5 1"""
          output = """3"""
          self.assertIO(input, output)
  
      def test_入力例_2(self):
          input = """4 10
  1 2
  2 1
  1 2
  2 1
  1 2
  1 3
  1 4
  2 3
  2 4
  3 4"""
          output = """4"""
          self.assertIO(input, output)
  
      def test_入力例_3(self):
          input = """10 4
  3 1
  4 1
  5 9
  2 6"""
          output = """3"""
          self.assertIO(input, output)
  
  
  if __name__ == "__main__":
      resolve()
  
problem_description: Statement
  
  There are N persons called Person 1 through Person N.
  
  You are given M facts that "Person A_i and Person B_i are friends." The same
  fact may be given multiple times.
  
  If X and Y are friends, and Y and Z are friends, then X and Z are also
  friends. There is no friendship that cannot be derived from the M given facts.
  
  Takahashi the evil wants to divide the N persons into some number of groups so
  that every person has no friend in his/her group.
  
  At least how many groups does he need to make?
samples: [{"input": "5 3\n    1 2\n    3 4\n    5 1", "output": "3\n    \n\nDividing them into three groups such as \\\\{1,3\\\\}, \\\\{2,4\\\\}, and \\\\{5\\\\}\nachieves the goal.\n\n* * *"}, {"input": "4 10\n    1 2\n    2 1\n    1 2\n    2 1\n    1 2\n    1 3\n    1 4\n    2 3\n    2 4\n    3 4", "output": "4\n    \n\n* * *"}, {"input": "10 4\n    3 1\n    4 1\n    5 9\n    2 6", "output": "3"}]