import sys
import pypyjit
import itertools
import heapq
import math
from collections import deque, defaultdict
import bisect

input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)
pypyjit.set_param('max_unroll_recursion=-1')


N = int(input())
adj = [{} for _ in range(N)]
for _ in range(N - 1):
    u, v, w = map(int, input().split())
    u -= 1
    v -= 1
    adj[u][v] = w
    adj[v][u] = w

child = [None] * N
cost = [None] * N
cost[0] = 0


def dfs(v, p):
    if v > 0:
        cost[v] = cost[p] + adj[v][p]
    acc = 1
    for d in adj[v].keys():
        if d == p:
            continue
        acc += dfs(d, v)
    child[v] = acc
    return child[v]


dfs(0, -1)
S = sum(cost)
ans = 0


def dfs2(v, p):
    global ans, S
    if v > 0:
        S += adj[v][p] * (N - 2 * child[v])
    ans += S
    for d in adj[v].keys():
        if d == p:
            continue
        dfs2(d, v)
    if v > 0:
        S -= adj[v][p] * (N - 2 * child[v])


dfs2(0, -1)
print(ans)