def longest_distance(graph):

indegree = [0] * len(graph)

queue = []

long_dist = [1] * len(graph)

for values in graph.values():

for i in values:

indegree[i] += 1

for i in range(len(indegree)):

if indegree[i] == 0:

queue.append(i)

while queue:

vertex = queue.pop(0)

for x in graph[vertex]:

indegree[x] -= 1

long_dist[x] = max(long_dist[x], long_dist[vertex] + 1)

if indegree[x] == 0:

queue.append(x)

print(max(long_dist))

graph = {0: [2, 3, 4], 1: [2, 7], 2: [5], 3: [5, 7], 4: [7], 5: [6], 6: [7], 7: []}

longest_distance(graph)