from collections import defaultdict, deque

n = int(input())
edge = defaultdict(list)
for _ in range(n - 1):
    u, v, w = map(int, input().split())
    u -= 1
    v -= 1
    edge[u].append((v, w))
    edge[v].append((u, w))

ans = 0
Parents = [-1 for _ in range(n)]
visited = set([0])
Que = deque([0])
Topo = []
while Que:
    curr = Que.pop()
    Topo.append(curr)
    for nex, _ in edge[curr]:
        if nex in visited:
            continue
        visited.add(nex)
        Parents[nex] = curr
        Que.append(nex)

Size = [1 for _ in range(n)]
for curr in Topo[::-1]:
    for nex, w in edge[curr]:
        if nex == Parents[curr]:
            continue
        ans += Size[nex] * (n - Size[nex]) * w
        Size[curr] += Size[nex]
print(2 * ans)