import queue
N = int(input())
edge = [[] for i in range(N)]
size = [1 for i in range(N)]
parent = [[-1,-1] for i in range(N)]

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

q = queue.Queue()
s = queue.LifoQueue()
parent[0] = [0,0]
q.put(0)
while q.qsize() > 0:
    f = q.get()
    for t,w in edge[f]:
        if parent[t][0] == -1:
            parent[t] = [f,w]
            q.put(t)
    s.put(f)
ans = 0
while s.qsize() > 0:
    f = s.get()
    size[parent[f][0]] += size[f]
    ans += size[f]*(N-size[f])*parent[f][1]*2
print(ans)