output_description: Print the maximum number of friendly pairs.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      a_1 b_1
      a_2 b_2
      :
      a_N b_N
      c_1 d_1
      c_2 d_2
      :
      c_N d_N
attempt: #!/usr/bin/python3
  # -*- coding:utf-8 -*-
  
  
  def main():
      n = int(input())
      lr = [list(map(int, input().split())) + [0] for _ in range(n)]
      lb = [list(map(int, input().split())) + [1] for _ in range(n)]
      lrb = sorted(lr + lb, key=lambda x: x[0])
      ignore = []
  
      rcnt = 0
      for x, y, c in lrb:
          if c == 0:
              rcnt += 1
          if c == 1:
              if rcnt == 0:
                  ignore.append([x, y, c])
              else:
                  rcnt -= 1
  
      #   lrb = sorted(lr + lb, key=lambda x: x[1])
      #   rcnt = 0
      #   for x, y, c in lrb:
      #     if [x, y, c] in ignore:
      #       continue
      #     if c == 0:
      #       rcnt += 1
      #     if c == 1:
      #       if rcnt == 0:
      #         ignore.append([x, y, c])
      #       else:
      #         rcnt -= 1
  
      print(n - len(ignore))
  
  
  if __name__ == "__main__":
      main()
  
problem_description: Statement
  
  On a two-dimensional plane, there are N red points and N blue points. The
  coordinates of the i-th red point are (a_i, b_i), and the coordinates of the
  i-th blue point are (c_i, d_i).
  
  A red point and a blue point can form a _friendly pair_ when, the x-coordinate
  of the red point is smaller than that of the blue point, and the y-coordinate
  of the red point is also smaller than that of the blue point.
  
  At most how many friendly pairs can you form? Note that a point cannot belong
  to multiple pairs.
samples: [{"input": "3\n    2 0\n    3 1\n    1 3\n    4 2\n    0 4\n    5 5", "output": "2\n    \n\nFor example, you can pair (2, 0) and (4, 2), then (3, 1) and (5, 5).\n\n* * *"}, {"input": "3\n    0 0\n    1 1\n    5 2\n    2 3\n    3 4\n    4 5", "output": "2\n    \n\nFor example, you can pair (0, 0) and (2, 3), then (1, 1) and (3, 4).\n\n* * *"}, {"input": "2\n    2 2\n    3 3\n    0 0\n    1 1", "output": "0\n    \n\nIt is possible that no pair can be formed.\n\n* * *"}, {"input": "5\n    0 0\n    7 3\n    2 2\n    4 8\n    1 6\n    8 5\n    6 9\n    5 4\n    9 1\n    3 7", "output": "5\n    \n\n* * *"}, {"input": "5\n    0 0\n    1 1\n    5 5\n    6 6\n    7 7\n    2 2\n    3 3\n    4 4\n    8 8\n    9 9", "output": "4"}]