from collections import defaultdict

class Graph:
    def __init__(self,vertices):
        self.graph = defaultdict(list)
        self.number_of_vertices = vertices

    def addEdge(self,to,fro):
        self.graph[to].append(fro)


    # A recursive function used by topologicalSort
    def topologicalSortUtil(self,v,visited,stack):

        # Mark the current node as visited.
        visited[v] = True

        # Recur for all the vertices adjacent to this vertex
        for i in self.graph[v]:
            if visited[i] == False:
                self.topologicalSortUtil(i,visited,stack)

        # Push current vertex to stack which stores result
        stack.insert(0,v)

    # The function to do Topological Sort. It uses recursive 
    # topologicalSortUtil()
    def topologicalSort(self):
        # Mark all the vertices as not visited
        visited = [False]*self.number_of_vertices
        stack =[]

        # Call the recursive helper function to store Topological
        # Sort starting from all vertices one by one
        for i in range(self.number_of_vertices):
            if visited[i] == False:
                self.topologicalSortUtil(i,visited,stack)

        # Print contents of stack
        print stack

g=Graph(6)
g.addEdge(5, 2);
g.addEdge(5, 0);
g.addEdge(4, 0);
g.addEdge(4, 1);
g.addEdge(2, 3);
g.addEdge(3, 1);

print "Following is a Topological Sort of the given graph"
#g.topological_sort()
g.topologicalSort()