# 部分木、子の数、DFS
# dfs2回は必要なかったので効率的な方法でやり直す

N = int(input())
edge_list = []
edge_dic = {}
edges = [[] for i in range(N+1)]
for i in range(N-1):
    u, v, w = map(int, input().split())
    edges[u].append(v)
    edges[v].append(u)
    edge_list.append((u, v, w))
    edge_dic[(u, v)] = w
    edge_dic[(v, u)] = w

child = [0]*(N+1)
visited = [0]*(N+1)

import sys
sys.setrecursionlimit(10**7)

def dfs(current):
    visited[current] = 1
    child[current] += 1
    
    for nxt in edges[current]:
        if visited[nxt] == 0:
            dfs(nxt)
            child[current] += child[nxt]
            
dfs(root)
#print(child)

ans = 0
for u, v, w in edge_list:
    mn = min(child[u], child[v])
    ans += mn*(N-mn)*w*2
print(ans)