output_description: Print the number of the edges that are bridges among the M edges.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N M  
      a_1 b_1  
      a_2 b_2
      :  
      a_M b_M
attempt: import copy
  
  n, m = map(int, input().split())
  node = [[0 for _ in range(n)] for _ in range(n)]
  aL = [0 for _ in range(m)]
  bL = [0 for _ in range(m)]
  for i in range(m):
      a, b = map(int, input().split())
      node[a - 1][b - 1] = 1
      node[b - 1][a - 1] = 1
      aL[i] = a
      bL[i] = b
  
  tmp1 = copy.deepcopy(node)
  chk = [0 for _ in range(n)]
  
  
  def DFS(x):
      chk[x] = 1
      for i in range(n):
          if chk[i] != 1 and tmp1[x][i] == 1:
              tmp1[x][i] = 0
              tmp1[i][x] = 0
              chk[i] = 1
              DFS(i)
      return chk
  
  
  cnt = 0
  for j in range(m):
      tmp1[aL[j] - 1][bL[j] - 1] = 0
      tmp1[bL[j] - 1][aL[j] - 1] = 0
      if sum(DFS(0)) != n:
          cnt += 1
      tmp1 = copy.deepcopy(node)
      chk = [0 for _ in range(n)]
  print(cnt)
  
problem_description: Statement
  
  You are given an undirected connected graph with N vertices and M edges that
  does not contain self-loops and double edges.  
  The i-th edge (1 \leq i \leq M) connects Vertex a_i and Vertex b_i.
  
  An edge whose removal disconnects the graph is called a _bridge_.  
  Find the number of the edges that are bridges among the M edges.
samples: [{"input": "7 7\n    1 3\n    2 7\n    3 4\n    4 5\n    4 6\n    5 6\n    6 7", "output": "4\n    \n\nThe figure below shows the given graph:\n\n![570677a9809fd7a5b63bff11e5d9bf79.png](https://img.atcoder.jp/abc075/570677a9809fd7a5b63bff11e5d9bf79.png)\n\nThe edges shown in red are bridges. There are four of them.\n\n* * *"}, {"input": "3 3\n    1 2\n    1 3\n    2 3", "output": "0\n    \n\nIt is possible that there is no bridge.\n\n* * *"}, {"input": "6 5\n    1 2\n    2 3\n    3 4\n    4 5\n    5 6", "output": "5\n    \n\nIt is possible that every edge is a bridge."}]