import sys
from collections import deque
input=sys.stdin.readline

N=int(input())
E=[[] for _ in range(N+1)]

Edge=[0]*(N-1)
for i in range(N-1):
    u,v,w=map(int,input().split())
    E[u].append(v)
    E[v].append(u)

    Edge[i]=(u,v,w)

root=1
Depth=[-1]*(N+1)
Depth[root]=0
Parent=[-1]*(N+1)
Parent[root]=0
Q=deque([root])

F=[[] for _ in range(N)]
F[0]=[root]
while Q:
    v=Q.popleft()

    for u in E[v]:
        if Depth[u]==-1:
            Depth[u]=Depth[v]+1
            Parent[u]=v
            Q.append(u)
            F[Depth[u]].append(u)

Descend=[1]*(N+1)

for G in F[::-1]:
    for x in G:
        if x!=root:
            Descend[Parent[x]]+=Descend[x]

X=0
for (u,v,w) in Edge:
    if Depth[u]>Depth[v]:
        u,v=v,u

    X+=w*Descend[v]*(N-Descend[v])
print(2*X)