Zadanie z grafem - Python

from sys import setrecursionlimit
setrecursionlimit(10001)

n = int(input())

graf = [[] for _ in range(n)]
distances = [[0 for _ in range(n)] for _ in range(n)]
visited = [False for _ in range(n)]
maximum = 0

for _ in range(n-1):
    a, b = map(int, input().split())
    graf[a-1].append(b-1)
    graf[b-1].append(a-1)


def DFS(v, parent):
    global graf
    global distances
    global visited
    global maximum
    global n

    if parent != -1:
        for i in range(n):
            if visited[i]:
                distances[i][v] = distances[i][parent] + 1
                distances[v][i] = distances[parent][i] + 1

                if distances[v][i] > maximum:
                    maximum = distances[v][i]

    visited[v] = True
    for neighbor in graf[v]:
        if not visited[neighbor]:
            DFS(neighbor, v)

DFS(0, -1)
print(maximum)