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: N=int(input())
  p_x=[0]*(2*N)
  p_y=[0]*(2*N)
  //N未満は赤い点
  for i in range(N):
  	x, y =map(int, input().split())
  	p_x[x]=i
  	p_y[y]=i
  //N以上は青い点
  for j in range(N):
  	x, y =map(int, input().split())
  	p_x[x]=N+j
  	p_y[y]=N+j
  
  pairs=N
  done_point=[]
  
  for i in range(2*N-1, 0, -1):
  	if p_x[i]<N:
  		pairs -= 1
  		continue
  	else:
  		blue_x=i
  		blue_y=p_y.index(p_x[i])
  		
  		for j in range(i-1, -1, -1)
  			if p_x[j] < N:
  				if p_x.index(p_x[j]) < blue_y:
  					if p_x[j] not in done_point:
  						done_point.append(p_x[j])
  						break
  				else:
  					pair -= 1
  					continue
  			else:
  				pair -= 1
  				continue
  
  print(pairs)
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"}]