from collections import deque

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

ans = 0
par = [-1]*n
vis = [0]*n
vis[0] = 1
q = deque([0])
topo = []
while q:
    now = q.pop()
    topo.append(now)
    for nex,_ in e[now]:
        if vis[nex]:
            continue
        vis[nex] = 1
        par[nex] = now
        q.append(nex)


size = [1]*n
for now in topo[::-1]:
    for nex,w in e[now]:
        if nex == par[now]:
            continue
        ans += size[nex]*(n-size[nex])*w
        size[now] += size[nex]
    
print(ans*2)