import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

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


par = [-1] * N
L = [0] * N
topo = []
q = [0]
while q:
    s = q.pop()
    topo.append(s)
    for t, c in G[s]:
        if t == par[s]:
            continue
        par[t] = s
        L[t] = c
        q.append(t)

size = [1] * N
ans = 0
for v in topo[::-1][:-1]:
    sz = size[v]
    ans += L[v] * sz * (N - sz)
    p = par[v]
    size[p] += sz
print(ans * 2)