N = int(input())
u = [0] * (N-1)
v = [0] * (N-1)
w = [0] * (N-1)
for i in range(N-1):
    u[i],v[i],w[i] = list(map(int,input().split()))
    
tree = [[] for _ in range(N+1)]
for i in range(N-1):
    tree[u[i]].append(v[i])
    tree[v[i]].append(u[i])
ko = [0] * (N+1)
q = []
q.append((1,0))
while len(q):
    now,parent = q.pop()
    if ko[now] == 0:
        ko[now] = 1
        q.append((now,parent))
        for i in tree[now]:
            if i != parent:
                q.append((i,now))
    else:
        for i in tree[now]:
            if i != parent:
                ko[now] += ko[i]
s = 0
for i in range(N-1):
    m = min(ko[u[i]],ko[v[i]])
    M = N - m
    s += m * M * w[i]
print(s * 2)