import sys
input = sys.stdin.readline

n = int(input())
g = [[] for _ in range(n)]
d = {}
for i in range(n-1):
    u, v, w = map(int, input().split())
    u, v = u-1, v-1
    d[(u, v)] = w
    d[(v, u)] = w
    g[u].append(v)
    g[v].append(u)

s = []
visit = [-1]*n
s.append(0)
order = []
par = [-1]*n
while s:
    v = s.pop()
    order.append(v)
    for u in g[v]:
        if u == par[v]:
            continue
        par[u] = v
        s.append(u)

ans = 0
c = [1]*n
order.reverse()
for v in order:
    if par[v] != -1:
        ans += (n-c[v])*c[v]*d[(v, par[v])]
        c[par[v]] += c[v]
print(ans*2)