output_description: Print the minimum number of operations required to achieve the objective.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      c_1 a_1
      c_2 a_2
      :
      c_{2N} a_{2N}
attempt: import sys
  
  input = sys.stdin.readline
  
  
  n = int(input())
  INF = 10**9
  info = [list(input().split()) for i in range(2 * n)]
  
  ind = {}
  for i in range(2 * n):
      if info[i][0] == "B":
          info[i] = (0, int(info[i][1]))
      else:
          info[i] = (1, int(info[i][1]))
      ind[info[i][0] * 10**5 + info[i][1]] = i
  
  ru_b = [[0] * (2 * n + 1) for i in range(n + 1)]
  ru_w = [[0] * (2 * n + 1) for i in range(n + 1)]
  for i in range(n + 1):
      for j in range(2 * n):
          col, num = info[j]
          if col == 0 and num > i:
              ru_b[i][j + 1] += 1
          elif col == 1 and num > i:
              ru_w[i][j + 1] += 1
      for j in range(2 * n):
          ru_b[i][j + 1] += ru_b[i][j]
          ru_w[i][j + 1] += ru_w[i][j]
  
  
  dp = [[INF] * (n + 1) for i in range(n + 1)]
  dp[0][0] = 0
  for i in range(n + 1):
      for j in range(n + 1):
          if i + 1 <= n and j <= n:
              bi = ind[i + 1]
              dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + ru_b[i][bi] + ru_w[j][bi])
          if i <= n and j + 1 <= n:
              wi = ind[10**5 + j + 1]
              dp[i][j + 1] = min(dp[i][j + 1], dp[i][j] + ru_w[j][wi] + ru_b[i][wi])
  
  print(dp[-1][-1])
  
problem_description: Statement
  
  There are 2N balls, N white and N black, arranged in a row. The integers from
  1 through N are written on the white balls, one on each ball, and they are
  also written on the black balls, one on each ball. The integer written on the
  i-th ball from the left (1 ≤ i ≤ 2N) is a_i, and the color of this ball is
  represented by a letter c_i. c_i = `W` represents the ball is white; c_i = `B`
  represents the ball is black.
  
  Takahashi the human wants to achieve the following objective:
  
    * For every pair of integers (i,j) such that 1 ≤ i < j ≤ N, the white ball with i written on it is to the left of the white ball with j written on it.
    * For every pair of integers (i,j) such that 1 ≤ i < j ≤ N, the black ball with i written on it is to the left of the black ball with j written on it.
  
  In order to achieve this, he can perform the following operation:
  
    * Swap two adjacent balls.
  
  Find the minimum number of operations required to achieve the objective.
samples: [{"input": "3\n    B 1\n    W 2\n    B 3\n    W 1\n    W 3\n    B 2", "output": "4\n    \n\nThe objective can be achieved in four operations, for example, as follows:\n\n  * Swap the black 3 and white 1.\n  * Swap the white 1 and white 2.\n  * Swap the black 3 and white 3.\n  * Swap the black 3 and black 2.\n\n* * *"}, {"input": "4\n    B 4\n    W 4\n    B 3\n    W 3\n    B 2\n    W 2\n    B 1\n    W 1", "output": "18\n    \n\n* * *"}, {"input": "9\n    W 3\n    B 1\n    B 4\n    W 1\n    B 5\n    W 9\n    W 2\n    B 6\n    W 5\n    B 3\n    W 8\n    B 9\n    W 7\n    B 2\n    B 8\n    W 4\n    W 6\n    B 7", "output": "41"}]