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: # -*- coding: utf-8 -*-
  
  
  def popcount(x):
      """xの立っているビット数をカウントする関数
      (xは64bit整数)"""
  
      # 2bitごとの組に分け、立っているビット数を2bitで表現する
      x = x - ((x >> 1) & 0x5555555555555555)
  
      # 4bit整数に 上位2bit + 下位2bit を計算した値を入れる
      x = (x & 0x3333333333333333) + ((x >> 2) & 0x3333333333333333)
  
      x = (x + (x >> 4)) & 0x0F0F0F0F0F0F0F0F  # 8bitごと
      x = x + (x >> 8)  # 16bitごと
      x = x + (x >> 16)  # 32bitごと
      x = x + (x >> 32)  # 64bitごと = 全部の合計
      return x & 0x0000007F
  
  
  N, M = map(int, input().split())
  
  ans_list = []
  for i in range(M):
      X, Y = map(int, input().split())
      X_bin = bin(1 << (X - 1))
      Y_bin = bin(1 << (Y - 1))
      com_bin = bin(int(X_bin, 2) | int(Y_bin, 2))
  
      flag = False
      for j in range(len(ans_list)):
          if (
              bin((int(X_bin, 2) & int(ans_list[j], 2))) == X_bin
              or bin((int(Y_bin, 2) & int(ans_list[j], 2))) == Y_bin
          ):
              ans_list[j] = bin(int(ans_list[j], 2) | int(com_bin, 2))
              flag = True
  
      if not flag:
          ans_list.append(com_bin)
  
  
  max_count = 0
  for j in range(len(ans_list)):
      count = popcount(int(ans_list[j], 2))
      if max_count < count:
          max_count = count
  
  print(max_count)
  
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"}]