boj1967.py

# from sys import stdin
# input = stdin.readline

# n=int(input())

# graph = [[] for _ in range(n+1)]

# for i in range(n-1):
#     a,b,c=map(int,input().split())
#     graph[a].append((b,c))
#     graph[b].append((a,c))

# dist=[0 for _ in range(n+1)]
# def dfs(start, graph, dis):
#     for a,b in graph[start]:
#         if dis[a]==0:
#             dis[a]=dis[start]+b
#             dfs(a,graph,dis)
    
# dfs(1,graph,dist)
# x=dist.index(max(dist))
# dist=[0 for _ in range(n+1)]

# dfs(x,graph,dist)
# print(max(dist))

import sys
sys.setrecursionlimit(10**6)
V=int(sys.stdin.readline())
 
matrix=[[] for _ in range(V+1)]
#입력받는 부분
for _ in range(V-1):
    a,b,c=map(int,input().split())
    matrix[a].append((b,c))
    matrix[b].append((a,c))
 
 
#첫번째 DFS결과
result1=[0 for _ in range(V+1)]
 
def DFS(start,matrix,result):
    for e,d in matrix[start]:
        if result[e]==0:
            result[e]=result[start]+d
            DFS(e,matrix,result)
 
DFS(1,matrix,result1)#아무노드에서 시작해준다.
result1[1]=0#루트노드가 정해져 있지않아 양방향으로 입력을 받기때문에 해당
 
 
tmpmax=0#최대값 구하기
index=0#최장경로 노드
 
for i in range(len(result1)):
    if tmpmax<result1[i]:
        tmpmax=result1[i]
        index=i
 
#최장경로 노드에서 다시 DFS를 통해 트리지름구하기
result2=[0 for _ in range(V+1)]
DFS(index,matrix,result2)
result2[index]=0
print(max(result2))