import sys

sys.setrecursionlimit(10 ** 7)

N = int(input())

G = [dict() for _ in range(N)]

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

p = -1
ans = 0


def dfs(v, pre=-1):
    global p, ans
    p += 1
    v_in = p
    for nx in G[v].keys():
        if nx == pre:
            continue
        dfs(nx, v)
    p += 1
    v_out = p
    if pre != -1:
        ans += (size := (v_out - v_in) // 2 + 1) * (N - size) * 2 * G[v][pre]


dfs(0)
print(ans)