from collections import defaultdict


N = int(input())
graph = defaultdict(list)
edges = []
for _ in range(N-1):
    a, b, x = map(int, input().split())
    a -= 1
    b -= 1
    graph[a].append(b)
    graph[b].append(a)
    edges.append((a, b, x))

subtree = [0] * N
def dfs(v, p):
    for next_v in graph[v]:
        if next_v == p:
            continue
        dfs(next_v, v)
    subtree[v] = 1
    for next_v in graph[v]:
        subtree[v] += subtree[next_v]

dfs(0, -1)
ans = 0
for a, b, x in edges:
    if subtree[a] < subtree[b]:
        # aよりbの方が根に近いところにある
        a, b = b, a
    ans += x * (subtree[b]) * (N-subtree[b]) * 2
print(ans)