output_description: Print the vertices numbers in order. Print a number in a line.
  
  If there are multiple possible solutions, print any one of them (the solution
  is judged by a special validator).
input_description: A directed graph $G$ is given in the following format:  
  $|V|\;|E|$  
  $s_0 \; t_0$  
  $s_1 \; t_1$  
  :  
  $s_{|E|-1} \; t_{|E|-1}$  
    
  
  $|V|$ is the number of vertices and $|E|$ is the number of edges in the graph.
  The graph vertices are named with the numbers $0, 1,..., |V|-1$ respectively.
  
  $s_i$ and $t_i$ represent source and target nodes of $i$-th edge (directed).
attempt: from sys import stdin
  from collections import deque
  n, e = map(int, stdin.readline().split())
  G = [[] for _ in [0] * n]
  indeg = [0] * n
  out = []
  V = [False] * n
  def bfs(s):
      dq = deque([s])
      V[s] = True
      while dq:
          u = dq.popleft()
          out.append(u)
          for i in range(len(G[u])):
              v = G[u][i]
              indeg[v] -= 1
              if indeg[v] == 0 and not V[v]:
                  V[v] = True
                  dq.append(v)
  def tsort():
      for u in range(n):
          for i in range(len(G[u])):
              indeg[G[u][i]] += 1
      for u in range(n):
          if indeg[u] == 0 and not V[u]:
              bfs(u)
      for i in range(len(out)):
          print(out[i])
  for _ in [0] * e:
      s, t = map(int, stdin.readline().split())
      G[s].append(t)
  tsort()
problem_description: Topological Sort
  
  ![](https://judgeapi.u-aizu.ac.jp/resources/images/IMAGE2_GRL_tsort)  
  
  A directed acyclic graph (DAG) can be used to represent the ordering of tasks.
  Tasks are represented by vertices and constraints where one task can begin
  before another, are represented by edges. For example, in the above example,
  you can undertake task B after both task A and task B are finished. You can
  obtain the proper sequence of all the tasks by a topological sort.
  
  Given a DAG $G$, print the order of vertices after the topological sort.
samples: [{"input": "6\n    0 1\n    1 2\n    3 1\n    3 4\n    4 5\n    5 2", "output": "3\n    1\n    4\n    5\n    2"}]