import sys
input = sys.stdin.buffer.readline
from collections import deque
import heapq
N = int(input())
E = [[] for _ in range(N)]
m = 10**3
for _ in range(N-1):
    u,v,w = map(int, input().split())
    E[u-1].append((v-1)*m+w)
    E[v-1].append((u-1)*m+w)

s = 10**6
q = deque()
q.append(0)
rnk = [-1]*N
rnk[0] = 0
while q:
    temp = q.popleft()
    v = temp//s
    r = temp%s
    for  e in E[v]:
        if rnk[e//m] >= 0:
            continue
        rnk[e//m] = r+1
        q.append(e//m*s+r+1)

h = []
num = [1]*N
for i in range(N):
    if len(E[i]) == 1:
        heapq.heappush(h, -rnk[i]*s+i)

used = [0]*N
used[0] = 1
while h:
    temp = heapq.heappop(h)
    v = temp%s
    used[v] = 1
    for e in E[v]:
        if used[e//m] == 0:
            num[e//m] += num[v]
            heapq.heappush(h, -rnk[e//m]*s+e//m)

ans = 0
for i in range(N):
    for e in E[i]:
        n = min(num[i], num[e//m])
        ans += n*(N-n)*(e%m)

print(ans)