import queue
N = int(input())
edge = [[] for i in range(N)]
size = [1 for i in range(N)]
depth = [[-1,i] for i in range(N)]
parent = [-1 for i in range(N)]
dist = [0 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()
q.put(0)
depth[0] = [0,0]
while q.qsize() > 0:
    f = q.get()
    for t,w in edge[f]:
        if depth[t][0] == -1:
            depth[t][0] = depth[f][0] + 1
            dist[t] = dist[f] + w
            parent[t] = f
            q.put(t)
depth.sort(reverse=True)
ans = 0
for tmp,i in depth:
    if parent[i] != -1:
        M = size[i]
        size[parent[i]] += M
        d = dist[i] - dist[parent[i]]
        ans += 2*M*(N-M)*d
print(ans)