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: import sys
  import copy
  if sys.platform =='ios':
  	sys.stdin=open('Untitled.txt')
  input = sys.stdin.readline
  def MAP(): return [int(s) for s in input().split()]
  
  N = int(input())
  A = [[False,MAP()] for _ in range(N)]
  B = [[False,MAP()] for _ in range(N)]
  
  #print(sorted(B))
  
  #below is incorrect 
  #count = 0
  #for b in B:
  #	delta = []
  #	for a in A:
  #		delta.append([a,[b[1][0] - a[1][0], b[1][1] - a[1][1]]])
  	#print(b,delta)
  #	cand = [[d[1][0]+d[1][1],d[0][1]] for d in delta if not d[0][0] and d[1][0] > 0 and d[1][1] > 0]
  #	if cand:
  #		cand = sorted(cand)
  #		print(cand)
  #		b[0] = True
  #		A[A.index([False,cand[0][1]])][0] = True
  #		count += 1
  
  #after reading answer
  count = 0
  for b in B:
  	cand = []
  	for a in A:
  		if b[1][0] > a[1][0] and b[1][1] > a[1][1] not a[0]:
  			cand.append(a)
  	cand = sorted(cand, key=lambda x:x[1][1], reverse=True)
  	if cand:
  		#print(b, cand[0])
  		b[0] = True
  		cand[0][0] = True
  		count += 1
  
  print(count)
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"}]