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)

q = deque()
q.append(0)
used = [0]*N
used[0] = 1
L = [0]
while q:
    v = q.pop()
    for e in E[v]:
        if used[e//m]:
            continue
        used[e//m] = 1
        q.append(e//m)
        L.append(e//m)

ans = 0
num = [1]*N
used = [0]*N
L.reverse()
for v in L:
    used[v] = 1
    for e in E[v]:
        if used[e//m]:
            continue
        ans += num[v]*(N-num[v])*(e%m)
        num[e//m] += num[v]

print(2*ans)