output_description: Find the minimum number of operations required to achieve the objective.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      x_1 y_1 a_1
      x_2 y_2 a_2
      :
      x_{N-1} y_{N-1} a_{N-1}
attempt: N = int(input())
  B = [0] * N
  for i in range(N - 1):
      x, y, a = map(int, input().split())
      B[x] ^= a
      B[y] ^= a
  D = {}
  for b in B:
      D[b] = D.get(b, 0) + 1
  D[0] = 0
  ans = 0
  first = 0
  for b in D:
      ans += D[b] // 2
      if D[b] % 2:
          first |= 1 << b
  
  A = [0] * (1 << 15)
  for i in range(1, 1 << 15):
      bit = i & -i
      l = len(bin(bit)) - 3
      A[i] = A[i ^ bit] ^ l
  
  memo = {0: 0}
  
  
  def dfs(state):
      if state in memo:
          return memo[state]
      cur = state
      res = 10**9 + 7
      while cur:
          if A[cur] == 0:
              res = min(res, dfs(state ^ cur) + bin(cur).count("1") - 1)
          cur -= 1
          cur &= state
      memo[state] = res
      return res
  
  
  ans += dfs(first)
  print(ans)
  
problem_description: Statement
  
  You are given a tree with N vertices. The vertices are numbered 0 through N-1,
  and the edges are numbered 1 through N-1. Edge i connects Vertex x_i and y_i,
  and has a value a_i. You can perform the following operation any number of
  times:
  
    * Choose a simple path and a non-negative integer x, then for each edge e that belongs to the path, change a_e by executing a_e ← a_e ⊕ x (⊕ denotes XOR).
  
  Your objective is to have a_e = 0 for all edges e. Find the minimum number of
  operations required to achieve it.
samples: [{"input": "5\n    0 1 1\n    0 2 3\n    0 3 6\n    3 4 4", "output": "3\n    \n\nThe objective can be achieved in three operations, as follows:\n\n  * First, choose the path connecting Vertex 1, 2, and x = 1.\n  * Then, choose the path connecting Vertex 2, 3, and x = 2.\n  * Lastly, choose the path connecting Vertex 0, 4, and x = 4.\n\n* * *"}, {"input": "2\n    1 0 0", "output": "0"}]